Refactor internals & external API

[snowsignal]

Sertain is a great library, but many internal changes can be made to make the code easier to understand. The API could also be refactored to make this library more than a nice wrapper for WPILib.
Here are the current sub-issues that I'm working on:

• Remove listeners and instead use hierarchical calling in Robot.kt
• Make the public function API for the new Robot abstract class

(More will be added)

All my changes can be found in the major-refactor branch on my fork.