Hotfix: unify and improve hotfix branch name logic

Now you can specify the full branch name, or the branch name without the
'hotfix-' prefix.

Equivalent:
   hotfix switch hotfix-blah-blah
   hotfix switch blah-blah
Merge hotfix-branch-name-tolerance (#55) into master

Hotfix: unify and improve hotfix branch name logic

Now you can specify the full branch name, or the branch name without the
'hotfix-' prefix.

Equivalent:

    hotfix switch hotfix-blah-blah
    hotfix switch blah-blah