tools/pydfu.py: Clean up syntax, update comments and docstrings.
tools/pydfu.py: Clean up syntax, update comments and docstrings.

Some parts of code have been aligned to increase readability.  In general
'' instead of "" were used wherever possible to keep the same convention
for entire file.  Import inspect line has been moved to the top according
to hints reported by pep8 tools.  A few extra spaces were removed, a few
missing spaces were added.  Comments have been updated, mostly in
"read_dfu_file" function.  Some other comments have been capitalized and/or
slightly updated.  A few docstrings were fixed as well.  No real code
changes intended.

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython