Bugfix to get_bytes and add section.data.

If get_bytes does not fill the list, get a slice of what was filled and
use that to convert to a bytearray. I still want to find a way to just
use a bytearray from the start. Luckily with the rest of this commit I
don't have a need to call get_bytes() on sections anymore.

Sections now have a data attribute which is a bytearray of the data that
makes up that section. This way you can just use section.data attribute
to get the entire contents and operate on it as you wish.

Make test.py use section.data to generate an MD5 of the section. It now
also prints the first 10 bytes of each section (if there are bytes).