ALSA MIDI backend: Quick and dirty fix for bogus zero-velocity note-off messages; output a note-on with zero velocity instead.

Added a "floatsize" method to [pdinfo]
Cleaned up the format specifier for [print] and gui_vmess
Got rid of unnecessary "l" in "%lg"

This makes it easier to point the gui dir at a local copy of the repo for
easier development. You can use this to make it easier to test out changes
to the GUI in purr-data/pd/nw.

Setting GUIDIR should even work if you haven't installed Purr Data to the
system. Just make sure the nw.js binary has been downloaded and expanded to
purr-data/pd/nw/nw. (This happens automatically when you build.)