feat: added 'changelog' root to req JSON

fix: added accept header

feat: changed the api endpoint to /api/changelogs

feat: not making any calls if api_host is not set

feat: instead of changing subdomain allow to set api_host

refac: it should be runtime dependency

feat: unsuccessful #save now returns false

test: removed unneeded setup before test

reformat: indent

fix: made #save return true on success

refac: renamed test file

refac: moved all the test to api tests

test: added WebMock.reset! to avoid failing expectations between tests

feat: change post to send JSON

feat: added #attributes