Use a C "union" to give both read (NMIST) and write (NMIRES) labels
to their shared register in ANTIC. (h/t @groessler).
Consolodate duplicated color definitions (HUE_..., COLOR_... and TGI_COLOR_...;
and the "_gtia_mkcolor()" macro), found in both "atari.h" and "atari5200.h",
moving it to "_gtia.h", which they both share (and which makes the most sense).
So far the joy_masks array allowed several joystick drivers for a single target to each have different joy_read return values. However this meant that every call to joy_read implied an additional joy_masks lookup to post-process the return value.
Given that almost all targets only come with a single joystick driver this seems an inappropriate overhead. Therefore now the target header files contain constants matching the return value of the joy_read of the joystick driver(s) on that target.
If there indeed are several joystick drivers for a single target they must agree on a common return value for joy_read. In some cases this was alredy the case as there's a "natural" return value for joy_read. However a few joystick drivers need to be adjusted. This may cause some overhead inside the driver. But that is for sure smaller than the overhead introduced by the joy_masks lookup before.
!!! ToDo !!!
The following three joystick drivers become broken with this commit and need to be adjusted:
- atrmj8.s
- c64-numpad.s
- vic20-stdjoy.s
