individual dirt stream start/stop

these changes to tidal.el allow you to start/set the first instance of d1-9 in the buffer using C-c C-1:9.

You can also stop the individual dirt streams with C-v C-1:9.

I am aware that I have added 18 functions to tidal.el and it could probably be consolidated to 2. If you would like me to figure out a bit more Emacs lisp and make another pull request I can.