Clean imports, lint aggressively, drop simplejson

Lots of small cleanups in preparation for the v0.1 release:

- Remove simplejson
- Remove unused imports
- Organize imports
- PEP8 all the things
- Pylint comments on log globals
- Consistent use of the exeption method on loggers
- Use *args for formatting log messages
- Move gevent subprocess patch to gunicorn.conf.py, where it belongs.

A note about simplejson: I've been convinced we should drop it.

Looking around the Web at benchmarks it appears that on Python 2.7+ the
standard library json module beats simplejson at encoding but loses
at decoding. As a server, we're likely to be doing more encoding than
decoding, but that's just my intuition. Finally, using simplejson
on Google App Engine is actually slower, since it won't include the
C speedups. In any case, it's simpler and cleaner code-wise to just
use the standard library version. Also, reports of inconsistent
handling of unicode in simplejson frighten me. The standard library
module has no such problem.