Fake6502: where the 6502 core's instructions come from.

Author:    Mike Chambers (miker00lz@gmail.com), Fake6502 v1.1, 2011
Licence:   public domain -- "This source code is released into the public domain, but if you use it please do give
           credit. I put a lot of effort into writing this!"  Credit is given here, in ../m6502_fake_machine.c's header
           and in the project's notices.
Upstream:  http://rubbermallet.org/fake6502.c

The pinned copy is the one EchoTalk vendors -- Jayson Smith's (@jaybird110127) Echo II / Textalker emulator, which
runs the real Textalker on this core, and from which this project takes its 6502:

  https://github.com/jaybird110127/echotalk
  revision  25ba18f850d9367f6690245b756234fe030c4ace
  file      third_party/fake6502/fake6502.c
  sha256    6356d2f4550c2f93645023df3eb8a7a3e22e04f3178a324baac34359e4fbb5de

EchoTalk's copy is upstream's plain core (its THIRD_PARTY_LICENSES.md: reduced back from a fork with debugger hooks)
with NES_CPU turned off, so decimal mode is honoured: the Apple II's 6502 is a MOS part, not a NES's.  EchoTalk is
BSD-3-Clause (LICENSE-EchoTalk-BSD-3-Clause.txt beside this file, its text as of that revision).  The lines copied
from the pinned file are Fake6502's own; EchoTalk's comment on NES_CPU is not among them, and its decision -- decimal
mode on -- is kept by never defining NES_CPU.

Nothing is copied unchanged.  ../extract_6502_machine.py copies exact line ranges into ../m6502_fake_machine.c (the
flag macros, push and pull, the addressing modes, every instruction including the undocumented ones, and the three
tables), refusing to run unless the source's sha256 is the one above and every anchor line is in place; every change
is named in the script and marked CHANGED in the output.

NOT taken: the globals, reset6502, nmi6502, irq6502, exec6502, step6502 -- our step driver in ../m6502.c replaces them
(CONTRACT.md 13).

To update: change SHA256 in the script, move any anchors, re-run it and the tests (test_m6502_contract.c,
m6502_controls.py), and record the new revision here.
