Add no_metadata flag for get_linked_docs

Add a flag no_metadata to get_linked_docs
- Return normally if it’s false
- Return only linked docs (no metadata information) if it’s true
Merge pull request #737 from nathando/develop

Add no_metadata flag for get_linked_docs
Update .travis.yml
Override Whitelisted Methods
[minor] [fixes] getdate, print heading as <h3>, prevent duplicate Not Permitted message