Rename build_in_place to build, and add a clean setup first.
DOC: 'from bigfloat import *' shadows 'round' as well as the already mentioned functions.
Various cleanups:

- Use setuptools instead of distutils.
- Add dependency on six, and use it for string types and integer
  types.
- Flake8 cleanups.
- Add .egg-info files directory to .gitignore.
Merge pull request #59 from mdickinson/flake8-cleanup

Various cleanups:
Merge remote-tracking branch 'origin/master' into feature/asprintf