Populate annotated tags message body during release

From https://github.com/tpope/git-bump/issues/7#issuecomment-46694410:
"If you save a GitHub Release for an annotated tag without setting the
title or body, they will be pre-populated from the tag's message."

This commit changes the release rake task to populate the message body
of the annotated tag that we create instead of opening the
CHANGELOG. These annotated tag message bodies can later be used to
prepopulate the release notes when creating a new release from a tag
on the Github web interface.
Remove CHANGELOG.md

Release notes after 2.4.0 (when Chocolate was open sourced) have been
manually copied over to the GitHub releases page.
Add missing full stop
Fix grammar in README
Merge remote-tracking branch 'origin/master' into replace-changelog-with-release-notes-in-annotated-tags

Conflicts:
	CHANGELOG.md
Merge pull request #70 from talk-to/replace-changelog-with-release-notes-in-annotated-tags

Replace CHANGELOG with release notes in annotated tags