Now the code has been split into several files to keep things better
organized.  Chip definitions are in chips.py, exceptions are in
exceptions.py, and LPC and friends are in lpc.py.  __init__.py has a new
function that provides the best way to create an LPC object, handling
all the boring bits of control, synchronization, and changing the type.

This commit adds a main function to the alpaca_isp package, which will
eventually allow flashing microcontrollers from the command line but for
now mostly parses command-line arguments.  There's more work to do
before I can get on with the real flashing (microcontroller-specific
stuff, Intel HEX stuff).