Humble contribution against LOGSTASH-948 joy-blocker

Add a new `make releaseNote` target to gather information from JIRA and merged pull requests in a releaseNote.html file

Add a proposal for a bot for : "Some kind of bot that will automatically ping pull requests saying a CHANGELOG entry is missing." Please try it, adopt it, crontab it ;)

Hope that helps restore the joy of releasing

Edit: forgot to mention that requires [octokit](http://me.wynn.fm/octokit/), so `gem install octokit` please