play/play — pull request #286 by holman (2013-06-30 16:09:23+00:00)
Title: Swap mpc out for ruby-mpd

[ruby-mpd](https://github.com/archSeer/ruby-mpd) has gotten a lot more mature since we looked at the state of libraries last year. Makes sense to switch, for a lot of reasons. Here's the benchmark comparison:

```
2.0.0-p195 in play/ on v3
› script/bm
user system total real
PlayQueue.now_playing 0.290000 0.780000 3.310000 ( 6.549815)
Song.find 4.350000 2.530000 9.620000 ( 18.218524)
Artist.all 1.790000 1.630000 6.050000 ( 8.355747)

2.0.0-p195 in play/ on ruby-mpd
› script/bm
user system total real
PlayQueue.now_playing 1.330000 0.180000 1.510000 ( 1.754545)
Song.find 4.050000 0.530000 4.580000 ( 11.256913)
Artist.all 4.690000 0.070000 4.760000 ( 5.591033)
```

And here's an informal comparison of a page request on an album listing page (where we currently have iterate and instantiate over all of an artist's songs):

```
v3: Completed 200 OK in 1259ms (Views: 997.5ms | ActiveRecord: 1.0ms | Mpd: 1262.4ms)
ruby-mpd: Completed 200 OK in 816ms (Views: 526.1ms | ActiveRecord: 5.7ms | Mpd: 136.5ms)
```