Update Changelog to include SHA

Added SHA to Chagelong
Update CHANGELOG.md
versioning/releasing docs
responding to review
Merge pull request #340 from Yelp/eliu_gh_338_define_and_doc_process_for_tagging_releases

versioning/releasing docs
Addressed all Scott's comments, updated documentation as requested.
Merge branch 'master' of https://github.com/Yelp/MOE into norases_255_create_epsilon_greedy_bandits