upd7810: use intermediate flip flops for extended timer/event counter

The extended timer/event counter uses intermediate flip flops (LV0 and
LV1) before writing the output to CO0 and CO1.

The introduction of LV0/LV1 addresses three issues:
- Level inversion occurs after the flip flop is output, not before;
- The intermediate flip flop can be altered without affecting the
  output of CO0/CO1;
- upd7810_write_EOM() didn't work properly when the level inversion
  bit was set along other bits.
peplus.c: Documentation update - NW
peplus.c: Slight update - NW
Merge pull request #43 from ramiropolla/upd7810

upd7810: use intermediate flip flops for extended timer/event counter
Merge pull request #44 from ramiropolla/steppers

steppers: add absolute position
Taito device tilemap assert fixes, and clean up of obsolete stuff (nw)
removed duplicated line of code (nw)
minor fixes
there were some typos in stopthie.bin (game still goes in an infinite loop tho)
(MESS) Added preliminary driver for TI Wiz-A-Tron. [Sean Riddle, hap]
pci: Add remapping notifiers [O. Galibert]
cbombers: fix TC0480SCP text layer colors [Alex Jackson]
undrfire.c, groundfx.c: improve documentation (TC0620SCC is the 6bpp tilemap chip) (nw)
ec1842: skeleton
gunbustr.c: use core palette handling (nw)
new clones
Ave Fenix (Recreativos Franco) [Enricnes]

(also verified on a PCB owned by Roselson)

this is the more polished of the Spanish bootlegs, possibly with a real license, even if the code is hacked from the original.
i82875p: Host bridge fun [O. Galibert]
dec8: lol 'colour overflow' (nw)
added comp4 and wizatron output_pla from Sean Riddle
new NOT WORKING
Sonic 2 (bootleg of Megadrive version) [caius]

needs correct coin logic (mcu sim?) hooking up for this bootleg, looks like a nasty hack, time counter is accelerated (so really you don't have long to complete the levels) sonic lives logo is hacked out and replaced with the credit display.

it boots with 2 credits, so you can play it right now, but can't add more credits.