Move documentation to GitHub (#59)

* Migrate docs to GitHub

* Try different layout for image examples

* Use code formatting for syntax examples

* Remove the since statements

Not helpful because the referenced releases are so old.  The 2.2
release was 9 years ago in 2014.

* Group methods with headings

* Add more method headings

* Hide the REST API documentation, not verified

* Another attempt to comment out a block

* Remove the REST description

Simplest form of comment, rely on git commit history

* Shorter message to match

* Narrower example

* Updates and corrections in changelog

* Optimize images

CHANGELOG.md

@@ -0,0 +1,138 @@
+# Changelog
+
+## Version 2.5 (Jun 24, 2019)
+
+-   Requires Jenkins 2.121.1 or later.
+-   New feature: `addHtmlBadge` is available [JENKINS-57917](https://issues.jenkins.io/browse/JENKINS-57917) -
+
+    ``` syntaxhighlighter-pre
+    manager.addHtmlBadge('<i>Italic text</i>');
+    ```
+
+-   groovy-postbuild no longer requires Overall/Administer permission: [JENKINS-54262](https://issues.jenkins.io/browse/JENKINS-54262) - It caused problems when used with [Authorize Project plugin](https://plugins.jenkins.io/authorize-project/)
+-   Suppress "WARNING: Avoid calling getLogFile on ..." when used in pipeline jobs.
+
+## Version 2.4.3 (Nov 18, 2018)
+
+-   FIX: removeSummary / removeSummaries doesn't work (throw UnsupportedOperationException) ([JENKINS-54184](https://issues.jenkins.io/browse/JENKINS-54184))
+
+## Version 2.4.2 (Aug 8, 2018)
+
+-   FIX: removeBadge / removeBadges doesn't work (throw UnsupportedOperationException) ([JENKINS-52043](https://issues.jenkins.io/browse/JENKINS-52043))
+
+## Version 2.4.1 (May 4, 2018)
+
+-   Have [Build Monitor Plugin](https://plugins.jenkins.io/build-monitor-plugin/) not cause errors.
+    ([JENKINS-50420](https://issues.jenkins.io/browse/JENKINS-50420))
+    -   Introduced fake `GroovyPostbuildAction`.
+    -   The feature of build-monitor to cooperate with groovy-postbuild doesn't work yet. It requires an upcoming release of build-monitor plugin to have it work again.
+
+## Version 2.4 (Mar 25, 2018)
+
+-   Requires Jenkins 2.60.3 or later
+-   Extract badge and summary features to [Badge plugin](https://plugins.jenkins.io/badge)
+    ([JENKINS-43992](https://issues.jenkins.io/browse/JENKINS-43992)).
+    -   You can use badge and summary features in pipeline only with badge-plugin. See [Badge Plugin](https://plugins.jenkins.io/badge/) for more details.
+-   Sanitize HTML in the badges.
+    -   You no longer be able to use HTML expressions in badge contents.
+-   **Don't upgrade to this version if you use [Build Monitor Plugin](https://plugins.jenkins.io/build-monitor-plugin/).**
+    -   Groovy-postbuild-2.4 breaks build-moitor-1.12 or earlier. Sorry.
+    -   Please postpone upgrading groovy-postbuild till fixing this issue:
+        [JENKINS-50420](https://issues.jenkins.io/browse/JENKINS-50420)
+    -   No new features in groovy-postbuild-2.4, and you can use
+        groovy-postbuild-2.3.1.
+        -   You can downgrade your groovy-postbuild in the Jenkins
+            Plugin Management page.
+        -   You can download earlier versions of groovy-postbuild from
+            "Archives" link in
+            <https://plugins.jenkins.io/groovy-postbuild>
+-   Some classes are migrated to badge-plugin. Please change classes in
+    your codes if you access those classes:
+
+    | Old Class                                                             | New Class                                             |
+    |-----------------------------------------------------------------------|-------------------------------------------------------|
+    | org.jvnet.hudson.plugins.groovypostbuild.GroovyPostbuildAction        | com.jenkinsci.plugins.badge.action.BadgeAction        |
+    | org.jvnet.hudson.plugins.groovypostbuild.GroovyPostbuildSummaryAction | com.jenkinsci.plugins.badge.action.BadgeSummaryAction |
+
+## Version 2.3.1 (Feb 7, 2016)
+
+-   Dependency to pipeline (aka. workflow) is optional
+    ([JENKINS-32589](https://issues.jenkins.io/browse/JENKINS-32589)).
+
+## Version 2.3 (Dec 27, 2015)
+
+-   Require Jenkins 1.609 or later
+-   Supports workflow
+    ([JENKINS-26918](https://issues.jenkins.io/browse/JENKINS-26918))
+    -   You can use `manager` in workflow scripts.
+
+## Version 2.2.2 (Oct 17, 2015)
+
+-   Added MIT License
+    ([JENKINS-21270](https://issues.jenkins.io/browse/JENKINS-21270))
+
+## Version 2.2.1 (Aug 18, 2015)
+
+-   Improved the behavior with [Template Project
+    Plugin](https://wiki.jenkins.io/display/JENKINS/Template+Project+Plugin)
+    ([JENKINS-21276](https://issues.jenkins.io/browse/JENKINS-21276))
+    -   Prior versions disturbed the execution of [Template Project
+        Plugin](https://wiki.jenkins.io/display/JENKINS/Template+Project+Plugin)
+        when the build was failed (even if the groovy script succeeded).
+
+## Version 2.2 (Dec 19, 2014)
+
+-   added getResult() as a whitelisted method
+    ([JENKINS-25738](https://issues.jenkins.io/browse/JENKINS-25738))
+
+## Version 2.1 (Oct 25, 2014)
+
+-   You can access other plugins in groovy scripts
+    ([JENKINS-14154](https://issues.jenkins.io/browse/JENKINS-14154))
+
+## Version 2.0 (Sep 21, 2014)
+
+-   Require Jenkins 1.509.4 or later
+-   Introduced [Script Security
+    Plugin](https://wiki.jenkins.io/display/JENKINS/Script+Security+Plugin).
+    ([JENKINS-15212](https://issues.jenkins.io/browse/JENKINS-15212))
+    -   You need reconfigure your projects or approve scripts. Have a
+        look at [\#Migration from
+        1.X](https://wiki.jenkins.io/display/JENKINS/Groovy+Postbuild+Plugin#GroovyPostbuildPlugin-Migrationfrom1.X)
+-   Added `manager.buildIsA(klcass)`.
+    ([JENKINS-24694](https://issues.jenkins.io/browse/JENKINS-24694))
+
+## Version 1.10 (July 26, 2014)
+
+-   added `envVars` and `getEnvVariable(key)`
+
+## Version 1.9 (April 29, 2014)
+
+-   [JENKINS-21924](https://issues.jenkins.io/browse/JENKINS-21924)
+    Support run for matrix parent
+-   change log level for each search from info to fine
+
+## Version 1.8 (August 22, 2012)
+
+-   Require Jenkins version 1.466 or later
+-   [JENKINS-13024](https://issues.jenkins.io/browse/JENKINS-13024)
+    Error in log indicating a missing descriptor
+-   added clickable badge
+
+## Version 1.7 (May 2, 2012)
+
+-   [JENKINS-13024](https://issues.jenkins.io/browse/JENKINS-13024)
+    Error in log indicating a missing descriptor
+
+## Version 1.6
+
+-   [JENKINS-9383](https://issues.jenkins.io/browse/JENKINS-9383)
+    security - restrict access to internal objects
+
+Can use now additional classpath for groovy postbuild scripts to have
+them in a central location. Scriptler Plugin?
+
+## Version 1.5 (November 5, 2011)
+
+-   Remove a html tag from the config page which causes an error on IE 7
+    ([JENKINS-10079](https://issues.jenkins.io/browse/JENKINS-10079))