Klein's codebase should meet the Twisted code standard

[hawkowl]

Rather than be a mismatched PEP8-Twisted code standard mess, it should be moved to meet Twisted's standard, with the old ones throwing deprecation warnings if possible.

[hynek]

We should limit this to APIs only btw; whitespace et al should be only fixed when adjacent code has been touched. Churn and all. Maybe enumerate the APIs that need fixing here and then open granular PRs for them?

[brighid]

Has the codebase drifted towards or away from Twisted's coding standards since 2014—is this still a concern, or is it down to a manageable level?

[wsanchez]

I made a 1.0.0 milestone and am moving this to that milestone.