Squashed 'third-party/bashflags/' changes from a5290fc..09603f7

09603f7 describe supported features
68deba7 add support for short flags parsing

git-subtree-dir: third-party/bashflags
git-subtree-split: 09603f72ffc3032f965467957969345f48996a6a
update bashflags (add support for short flags)