Use the newer sync sequence. Refactor the pulse() function to make
it somewhat generic, so we can use it without worrying about writing
the exactly right number of bytes.
This seems to get STC15W4 series chips working.
Split up single script into a package with multiple modules.
Also add a setuptools control file. With this, stcgal can be
installed like any other program. It's still possible to launch
from the sources directly. stcgal.py has been converted into a
simple launcher.
v2: fix imports
