Refactoring

[bakermoran]

This is a large PR that mostly refactors the code into different files and functions -- in short makes it more of a production package.

• Separate like functionality from the main class file into separate files for each functionality.
• Move an import into the init file for easier importing for the end user.
• Rename public functions to fit() and plot() for more pythonic code.
• Refactor tests into a controller file (git ignored) and a tests file, so as to not have to commit/delete changes when changing which tests are run
• Adds better doc strings
• Makes package more scalable/allows for addition of additional classes in the future