Rename mplayer.*.{rc,po(t)} to mpc-hc.*.{rc,po(t)}. (WIP)

Also use more appropriate language codes for the language DLLs.
Rename mplayer.*.{rc,po(t)} to mpc-hc.*.{rc,po(t)}.

Also use more appropriate language codes for the language DLLs.
Merge branch 'master' of https://github.com/mpc-hc/mpc-hc