Preliminary format refactor
The branch for the other PR was messed up, so I created a new one.

- [x] based on discussion here: https://github.com/pandas-dev/pandas/pull/20032#pullrequestreview-101917292
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

This PR splits the various formatters into different files so that it's easier to refactor a specific formatter. 
lgtm. ping on green. thanks @shangyian 