Divided program in more source files.
debug
Added shell_ui and synth module

shell_ui contains the shell loop and function to acquire paramethers
from user and set them, synth module contains function for wave
synthesis and computation of note frequencies (i left the array
note_frqs in the main source file cause seems that jack can read fast if
it's there)
Adjusted some data type
Added data.c and data.h

Some variables need to be global so i putted them in a single source
file for a cleaner code.
Added control for midi channel

Now the program listen only on the specified midi channel
Added handling of program change and volume change

Now the program can handle program change and volume change from midi
divided volume from max_amplitude

so the user can set a master amplitude from shell and modulate volume with midi
Merge pull request #2 from MicheleSr/development

Development