Emacs dirtree recipe

The dirtree currently in el-get does not give you a tree view of directories.  This does, and in the documentation about it they are all referred to as dirtree which is confusing.  I hope the description will make it clear what this one is for.

Thanks, and I hope this helps others who have been searching for a directory tree in emacs.

And thanks to Ye Wenbin for creating it and zkim on github for having an accessible repo.