Release 0.8.0

• changes maven groupId from software.amazon.ion to com.amazon.ion to be consistent with other Ion-related open source projects (#105)
• changes java package names from software.amazon.ionschema to com.amazon.ionschema (#105)
• updates ion-java dependency to version 1.4 (and use of the com.amazon.ion namespace)
• adds Schema.plusType() (#73)
• adds support for schema import (#1)
• adds support for the document type (#11)
• adds support for using an import as a type reference (#66)
• adds support for escaping / and " chars in regexes (#77)
• adds support for regex multiline mode (m flag) (#78)
• allows a type to reference a type defined beneath it (#59)
• defines a schema for ISL using ISL (#10)
• updates the ordered_elements constraint to follow multiple solution paths (#108)
• various documentation, testing, and code quality improvements

Bugs fixed:

• confusing error when creating type definition referencing undefined type (#55)

Associated milestone: M3

Full list of changes: v0.7.0-alpha...v0.8.0-alpha