Applies minor refactoring and cleanup.
Renames BOR instruciton to OR.
Adds more Instruction unit tests.
Fixes Cpu.skipBranches to account for PC exceeding memory bounds.
Renames IDevice.Interrupt to IDevice.Int.
Just because.
Add InvalidAddressException. Used when the CPU encounters
an out-of-bounds PC value.
Performs some minor cleanup.
Add error.cs file and set standard file header for this project to
include the license.
Implement a bunch more unit tests for CPU instructions.