resolves #297 support for abstract and partintro

- support for abstract and partinfo style on open block
- support for abstract and partinfo style on paragraph
- wrap text in paragraph with complex block style in simpara
- fix missing @ on field reference
- fix missing endlines for blocks output by result methods
- add text support to open block
- backend optimizations
validate partinfo & abstract usage; optimize templates

- validate that partinfo and abstract are used in proper location
- add tests for partinfo and abstract validations
- add argument to attr? & attr methods to look on node only
- don't look for style attribute on document
- template cleanups
Merge pull request #305 from mojavelinux/partintro-abstract-support

resolves #297 support for abstract and partintro