Support for semver

[willgopublic]

Please add support for semver.org version tagging/naming for hotfixes.
e.g. git flow hotfix start should (if configured to use semver) create a branch named hotfix/a.b.c where c is previous value for c plus 1 .

git flow hotfix start \
$(git tag --sort=taggerdate | tail -1 | cut -d '.' -f 1,2 )'.'\
$(( $( git tag --sort=taggerdate | tail -1 | cut -d '.' -f 3 ) + 1 ))