Add missing tests

[hmil]

TODO:

• [x] test comments
  • [x] post / edit
  • [x] vote
• [x] test reviews
  • [x] post / edit
  • [x] vote
• [x] test api
  • [x] review api
  • [x] comment api
  • [x] vote api
• [x] clean api/utils.coffee
• [x] document utilities (both api & integ)

[hmil]

This PR should fix #94

[hmil]

close #63 (good testing = no 500 = no need for #63 )

[hmil]

Won't test comment delete feature for the following reasons:

• Forces to reset the database before each test
• Cannot test based on status code so the test itself would be hacky anyway (sth like assertBodyDoesntContain...) for a piece of code which has little to no chance of breaking it's not worth.