Pretty-tables

- Removes the validation requiring the colors array to match the length of the columns. When no color is passed for a column, the formatting will be reset to default
- Introduces the `Colors.none` enum to be used instead of `None` on the colors array

- Drops support for Python 3.7

- Fixes the reference to `py.typed` in `setup.py` so packages can pull in the typing of this package properly

- Adds `mypy` to run type checking and publishes types with new `py.typed` file

- Adds missing `__all__` variable for imports

- Refactored the entire app to be more straightforward to use. Create a new table by calling `pretty_tables.create()` and pass in your arguments
- Added missing white and black colors, changed how to invoke the colors (now `pretty_tables.Colors.blue` instead of `pretty_tables.TableColors.OKBLUE`)
- Validate `color` parameter which was previously skipped
- Overhauls documentation providing all customization options (closes 2)