Add API support for passing min_width parameter to simple_separated_format

[stefansjs]

Modifies TableFormat to take optional parameters, and passes kwargs from simple_separated_format to TableFormat

[astanin]

This project uses Appveyor to run tests on Windows. Please remove edits of the CI files.

Also rewriting most of the assertions in the test files will probably create conflicts with other PRs. And it's difficult to see if there are breaking changes and what exactly has changed. Please narrow down your changes to only what is relevant to this new feature.