add option 'nyan-music-player' along with support for mpv

[ksqsf]

I use mpv instead of mplayer so I changed nyan-mode a little bit.

I hope this change is small enough not to disturb mplayer users. :-)

[ParetoOptimalDev]

Does this work? Locally I use:

(start-process-shell-command "nyan-music"
                             "nyan-music"
                             (concat "mpv --no-video --loop=inf " nyan-music))

[ParetoOptimalDev]

Or for a copy paste solution if/until this gets merged:

(use-package nyan-mode
  :config
  (defun my/nyan-start-music ()
    (unless nyan-music-process
      (setq nyan-music-process
	    (start-process-shell-command
	     "nyan-music"
             "nyan-music"
             (concat "mpv " nyan-music " --loop=inf")))))
  (advice-add 'nyan-start-music :override 'my/nyan-start-music)
  (nyan-mode 1)
  (unless (nyan--is-animating-p) (nyan-start-animation))
  (nyan-start-music))