w65c816 0.1.17

An emulator for the WDC W65C816S, a 16-bit derivative of the 6502.
Documentation
# W65C816
An emulator for Western Design Center's W65C816S, a 16-bit derivative of the
WDC W65C02S, which is itself a derivative of the MOS 6502.

I'm developing this as there doesn't appear to be any existing standalone '816
cores in Rust, and certainly not at the level of emulation I'm doing
(though we can go deeper!). For other programming languages, 816 cores seem
pretty sparse, and as far as I know, none provide a bus-accurate cycle-accurate
emulator with all signals.

# Testing
This core has been validated against
[this test suite](https://github.com/SingleStepTests/65816) and passes all
tests. The core has not been validated against actual hardware.

Current plans:
- [x] continue adding instructions
- [x] continue adding addressing modes
- [x] ensure ABORT is implemented for all instructions
  - [ ] ensure ABORT is implemented *correctly* (check with a real '816)
- [x] tests, tests, and more tests
  - [ ] ideally generate tests from a real '816.