ZERICO2005

Added multiply high signed/unsigned routines. These can be used to optimize division by a constant. `__smulhu` is optimized, but the rest are not well optimized. They use the exact same...

We should access the contents of `` and `` in assembly; And perhaps we should also allow some of `ti84pceg.inc` to be accessible in C as well. For example: ```asm...

The following appear to be missing from ``: - `freopen` - `ungetc` (probably as a user defined weak function if it doesn't make sense in fileioc) - `setbuf` - `setvbuf`...

Currently, `gfx_CopyRectangle` does not allow for two buffers to overlap. However, it does not appear to be too difficult to allow overlapping buffers. This basically means implementing `gfx_CopyRectangle` like `memmove`...

I was able to save 1 byte in the `dzx0_turbo` routine from the optimizations pointed out here https://github.com/einar-saukas/ZX0/issues/32. Otherwise the speed is the exact same. This 1 byte saving can...

I have found a small optimization to `dzx0_turbo`. Changing `ld a, $80` to `inc c \ scf` allows us to skip a few instructions. I believe this optimization can also...