Added description parameter support to Create and Update MR API endpoints (issue-110).
Added tests of Create and Update MR description.
Merge branch 'issue-110' of https://gitlab.com/gmessner/gitlab-ce into gmessner/gitlab-ce-issue-110

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Conflicts:
	CHANGELOG
Merge branch 'gmessner/gitlab-ce-issue-110'