py: Rename byte_code to bytecode everywhere.

examples/micropython.py

py/bc.h

py/compile.c

py/emitbc.c

py/emitcpy.c

py/emitglue.c

py/emitglue.h

py/mpconfig.h

py/objfun.c

py/objgenerator.c

py/qstrdefs.h

py/showbc.c

py/vm.c