[feat-req] add all missing commands from mpc, minor improvement

[ozone89]

First thing first, thank you for the hard work you're putting into this project :D

As per title, it'd be nice to have the command set on par with mpc

List can be found here https://helpmanual.io/help/mpc/ or via mpc help

In particular, would be nice to have at least cdprev and toggle, as it would simplify some coding

as an example, I have managed to implement the former as

if float(client.status()['elapsed']) < 5:
        client.previous()
else:
        client.play(client.status()['song'])

also, little improvement would be to have the value of the fields returned as the proper type

[Mic92]

Are those also in the mpd protocol?

[Mic92]

I prefer to not make library more complex than necessary.