Mpd support

[tramhao]

This support play music by mpd and can lower cpu usage during playing dramatically. When playing with beep, my gotop cpu usage of gomu is around 20%, but when use mpd, cpu usage of gomu is 2-3 percent, and mpd use another 3 percent.
You'll need to modify configuration to use it

# Backend music playing server, default is beep, mpd is optional
backend_server	= "mpd"
# mpd connect string
mpd_port	= "localhost:6600"

[issadarkthing]

This is cool! I will look at it

[tramhao]

Problem with album photo:
When press skip continuously, following error message will appear:

[xgbutil] xwindow.go:326: BadWindow {NiceName: Window, Sequence: 395, BadValue: 44040219, MinorOpcode: 0, MajorOpcode: 4}

It seems that the album photo destory too fast. Trying to figure out how to fix it.

[tramhao]

Problem with album photo:
When press skip continuously, following error message will appear:

[xgbutil] xwindow.go:326: BadWindow {NiceName: Window, Sequence: 395, BadValue: 44040219, MinorOpcode: 0, MajorOpcode: 4}

It seems that the album photo destory too fast. Trying to figure out how to fix it.

should be fixed now.

[tramhao]

Please don't merge it, have some serious problems.

[tramhao]

Seems working now.

[tramhao]

In order to fix data race, a lot of getters and setters are used. Any suggestion for improvement?