[WIP] Add "create release" feature#11

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hiroshi wants to merge 6 commits intox-motemen:masterfrom

hiroshi:create_release

Commits on Jan 14, 2015

Commits on Jan 15, 2015

Fix that --release latest (default behaviour) doesn't work.
hiroshi
committed

Commits on Jan 17, 2015

No need to `git update` for --release.
hiroshi
committed

Commits on Feb 24, 2015

Use pull.title for release.name instead of "time (PR number)".
hiroshi
committed

Commits on Feb 27, 2015

Use pull.title as a tag name if config git-pr-release.release.tag == pull.title.
hiroshi
committed