update to v0.7 of dfm

* dotfiles repository can now be outside of home directory, using $DFM_REPO
* add help subcommand and refactor help handling
* make 'help' the default subcommand (seth--)
* better parsing of arguments to preserve all arguments passed through to git subcommands
remove mention of personal dotfiles, they are in another repo
Merge remote-tracking branch 'upstream/master' into brett-common