add proof of concept for path flags API and add git modified flags
allow flags to be scoped to a plugin

Add new FlagSet class and init each Path with one.

Call Path.flagSet.addFlag(scope, flag) instead of Path.addFlag(flag)
fix a retarded bug with FlagSet.clearFlags
add `.refreshFlags()` to path/dir/file objects

This will trigger the path refresh callbacks without refreshing the
path's from disk (which takes ages)
Merge branch 'master' into expt_add_path_flags_and_git

Conflicts:
	autoload/nerdtree.vim
	lib/nerdtree/creator.vim
Merge branch 'master' into expt_add_path_flags_and_git
Merge branch 'master' into expt_add_path_flags_and_git
remove testing git plugin