Prettypandas

Major refactor of library oriented around extending Pandas DataFrame rather than implementing a `Styler` class.

* Cleaned up internal aggregation API
* Fixed bugs around formatters
* Added functionality to put data back to `DataFrame`
* Better interoperability with Pandas style API
* Safer fluent API (now adjustments only modify a copy)
* Updated documentation

* Removed CSS/styling components
* Removed Pandas Styler internals

Between Pandas Style API and Jupyter Notebook default styling for tables Pandas has good defaults and the ability to easily customize the look and feel of DataFrames. Because of that I've removed the styling components from the library and users should use `DataFrame.style` from this point on.

This is a bug fix release. The Pandas style API had issued breaking changes to this library in 0.18.1 (which was to be expected, the Pandas Style API is still a provisional API and subject to breaking changes).

It's recommended that everyone update to this version which should maintain compatibility with both APIs.

- Added localization support for currencies and percentages
- Deprecated `as_money` in favour of `as_currency`
- Fixed multi-index bug
- Switched documentation to autodocs