expand Util.Pack/Unpack to allow repeat counts for non-strings

expand Util.Pack/Unpack to allow repeat counts for non-strings
changed so that TestPack() is run only on --test
WIP: p() to mimic libpebble's p.py
code cleanup, added reinstall/unload/load to p()

Add Util.CreateFormat() to create an unpack format string for structs
make more calls use Util.Unpack()