Get rid of bundled beep
Use "Instant Message Notification" system sound on Windows, use gdk_beep() on Unix

Note: gdk_beep() is expected to be replaced with libcanberra stuff.
Fix unused variable
use libcanberra for beeps
Remove extra omitalerts check
udpate travis build w/ canberra
Let's just say the word
Use canberra for files
clean up canberra code
More cleanup
Escape all the things
Remove dead code for sound_command
Use regular canberra not gtk
Update .travis.yml
Fix spacing
Store just the filename if the sound file comes from the default sound dir

And get rid of some hardcoding while we're at it
Eliminate compiler warning

free() requires stdlib.h