Add rendering of enum constant value doc comments.

(picked #24)
Fix #21, incorrect javadoc summary lines

- Use simpler section & paragraph output templates so javadoc can correctly
  extract the first sentence for its package, class & method summaries.
- Templates are bundled as resources in asciidoclet.jar then written to a
  tmp dir on javadoc execution where Asciidoctor can find them.
- Added Guava dependency to simplify copying of resources.

(picked #23)
Use Guava's File.toString() to read overview file.