Create a register overflow exception
Change register implementation to has-a model

Partial re-implementation of register class hierarchy such that specific
register types implement a has-a relationship with GenericRegister.
Although this prevents using polymoprhism at the moment, dealing with the
different data sizes of their internal storage was going to be a pain
anyway.
Use static final values for max and min as opposed to hardcoded values.
Add missing GPL2 license comments
Create exception for register underflows
Add underflow exception to setValue.
Make inc/dec stack pointer operation smarter.

Use getValue and catch all over/underflow exceptions.
Teach push and pop to be smarter

Use the updated register interactions.
Document CPU6502.

Javadoc needed to happen.  Do it.
Document  GenericBus.

Javadoc needed to happen.  Do it.
More documentation.

Finish documenting the main classes at their current state.
Create XML representation of a register

Add getAsXML to convert a register to an XML representation for debugging purposes.
Teach Register8Bit to pass through getAsXML calls

GenericRegister handles this functionality, so pass it along.
Create Exception for errors in generating debug information.

Creating debug info can generate exceptions from multiple sources- encapsulate them for callers.
Teach CPU classes that they can output debug XML.