ant: Add ant build logic for sphinx documentation
travis: Use ant to build documentation
travis: Install ant-contrib
travis: Install ant-optional
ant: Move taskdef to rules.xml
travis: Explicitly set CLASSPATH
ant: Add linkcheck targets
README: Document ant usage
Remove formats & contributing from build.xml

These document sets don't exist on this branch, they are only maintained on develop
Delete contributing/build.xml
Delete formats/build.xml
Merge pull request #746 from hflynn/rebased/dev_5_0/ant-build

Use ant to build sphinx docs (rebased onto dev_5_0)