Python 3 compatibility

[Snigelson]

Should still be backwards compatible with Python 2

[florisla]

This avoids syntax errors on Python 3, but it doesn't work yet. Main things that need to change is to use bytes/bytearray when working with data.

I have a port to Python 3 in the works (tested read/erase/write/verify) but I haven't yet created the commits for it.

[kuraga]

@florisla could you please publish them?

[rickbase1]

@florisla I second Kuraga's request to publish a python3 compatible version of this tool as soon as you can. Thanks!

[royberkeveld]

I also needed Python 3 compatibility, so I fixed it before discovering you were already working on it. I tested read/erase/write/verify myself. Here is a gist.

[florisla]

I've finally cleaned up my Python 3 branch. It works very similar to @royberkeveld 's of course...

See https://github.com/florisla/stm32loader

[susundberg]

Please merge changes.

+1 for @florisla - i used your version and it works fine with my configuration.

[florisla]

@susundberg This repository has seen no updates for four years now, I think we can say it's not maintained anymore. You're welcome to use my fork, I'll try to maintain it.