Code PEP8'ed and linted

[etingof]

This branch has asn1ate codebase linted and PEP8'ed. Among other changes:

• assert statements replaced with raise because assert gets removed from optimized byte code.
• references to undefined local variables fixed
• a few typos fixed here and there

[kimgr]

Looks great, thanks!

Please find some nits inline.

[etingof]

Addressed most of your comments.

[kimgr]

Thanks! A few more comments/questions, but I'm generally happy with this.

[kimgr]

I suqashed this and pushed as 03e3a64d1755be395ace09c427f37f8a1cbbbbe5. Many thanks for the cleanup!

I'll make a couple of follow-up changes (there were still a few mentions of 'implicity') shortly.