memarea: Always use bytearray instead of bytes for Py2 compatibility reasons

Signed-off-by: Michael Buesch <m@bues.ch>
coreserver: Always pack memarea data as bytes to avoid Py2 compatibility issues

Signed-off-by: Michael Buesch <m@bues.ch>
wordpacker: Add assertion

Signed-off-by: Michael Buesch <m@bues.ch>