Added pep8 tox environment

[skudriashev]

It is very useful to check against pep8 rules along with other testing.

[skudriashev]

Guys, shell we add this?

[mahmoudimus]

@skudriashev thanks for this :) I'll see how this goes. I typically think quality and testing should be two different jobs.

Testing:

• Iterate, iterate, iterate until you're happy

Quality:

• Getting ready to ship it.

Though, I'll see how this goes.

Thanks!