Migrate documentation to MKDocs

[jensschuppe]

In order for the extension's documentation to be published on https://docs.civicrm.org, it needs to be converted to MKDocs format.

Additionally, the current documentation should be revised for changes in described functionality or installation.

[jensschuppe]

0dea0f5 migrates the English version of the current documentation to MKDocs.

@bjendres This should be checked for accuracy and obsolescences for the current version of the extension.

The German documentation can then be adapted afterwards. Unfortunately, different languages need their own documentation repository.

[jensschuppe]

This might use an update for the new features in 1.6 and 1.7

[jensschuppe]

Documentation is missing for the new features:

• unlockable fields for receipted contributions
• watermark presets
• e-mail exporter
  • Bounce handling
  • configurable "From" e-mail address
• more tokens (Smarty variables) in templates
• hooks
• currency selection
• anything else?

Installation instructions seem outdated as well.

Also, screenshots and step-by-step tutorials or at least an explanation of all configuration options and functionalities would be nice.

[grischard]

Currency selection is quite big - I'm currently avoiding this plugin because we receive donations in multiple currencies. Impatient to see the updated documentation :)

[jensschuppe]

Since version 2.0 made major changes to the configuration UI, this should also go into the new MKDocs documentation.

[jensschuppe]

Migration to MKDocs has already been merged for 2.1.x, see #160 for actual updates of the docs.