Add support for new commands in mpd.

[bens]

mpd 0.14 added the "idle" command and added an optional position argument to "addid". mpd 0.15 added sticker commands, "consume", and "single". Added optional range arguments to "playlistinfo" and "move" commands.

http://www.musicpd.org/doc/protocol/

[bens]

When #7 gets done, these new commands should take the version into account and not send unknown commands to an old server.

[joachifm]

New commands and ranged playlist positions are available in the mpd-0.15 branch of git://github.com/joachifm/libmpd-haskell.git

I think it would be better to split out a legacy branch that would remain compatible with 0.13.0 instead of having the library deal with multiple versions of the protocol at runtime. It might work out in trivial cases, but it seems to me that it's possibly too much of a hassle to do it for everything.

[joachifm]

Done in my repo (git://github.com/joachifm/libmpd-haskell.git)