Move routing src/snk creation into alsa.c from window-routing.c.
Move port_category and port_num from struct routing_snk to struct
alsa_elem.
Handle ALSA elements with two values.
Handle controls labelled as 1L and 1R instead of 1 and 2.
Rather than having widget/widget2/widget_callback fields in the struct
alsa_elem, have a list of callbacks and allow private data to be
passed to callbacks.