Data mentions facebookposts and facebookcomments

### Added
- data/mentions/facebookcomments endpoint
- data/mentions/facebookposts endpoint

### Updated
- removed redundant else as per rubocop error
`lib/bwapi/error.rb:28:7: C: Redundant empty else-clause.`

Tested this locally
```
[61] pry(main)> if false
[61] pry(main)*   true
[61] pry(main)* elsif false  
[61] pry(main)*   true
[61] pry(main)* end  
=> nil
```

Ran rubocop and rspec as per guidelines
Also ran against current work to test methods

This appears to be the way we do it with the 'fulltext' endpoint which is what i was going off of
However topsites becomes top_sites and bulkactions to bulk_actions 

I will change this and update full text at the same time