Allow a regex to enforce feature branch naming rules

[steppinrazor]

Sometimes in enterprises you may want to enforce feature branch naming standards such as possibly based on tracking codes (like Jira, Mantis, YouTrack...) and/or you want to restrict summary message lengths - these become relevant when running merge --squash and the feature branch name represents the commit on develop/master.

See #37

[aleksandr-m]

1.5.0 is out.