Input Handler Documentation

I found that the number of events that appeared on any object that received inputs was high and the descriptions were almost identical. They were so long that any changes (ex: sol.main does not receive game command events) were obscured.

So I created the idea of an input handler, documented it in sol.input and then used cross references to make sure you can find your way back and forth.

Custom state is also listed as an input handler, it was not mentioned in the input documentation before. Other than that orthogonal fix the main benefit is clarity by reducing unnecessary duplication and putting more information about input in one place.