v68: new CUI emulator with sound

[vampirefrog]

Howdy! Again an older project, a tool similar to run68 but with sound capability.

I got it to the point where it can run mxdrv and pcm8a and play some MDX files. It builds and runs on linux and in msys. There are some tests in the tests/ folder.

Some features:

- Using musashi 68k emulator
- DOS calls: EXIT, EXIT2, PRINT, PUTCHAR, KEEPPR, SUPER, IOCTRL, SETBLOCK, MALLOC, FPUTS, VERNUM, GETDATE, GETTIME, GETTIM2, CREATE, OPEN, CLOSE, WRITE, READ, FGETC, SEEK, INTVCS, INTVCG, PRNSNS, CONCTRL, NAMECK, GETPDB, CURDRV, CHGDRV
- IOCS calls: B_PUTC, ONTIME, B_MEMSTR, ADPCMOUT, B_INTVCS, B_LPEEK, B_BPEEK
- FE calls: LTOS, CLMOD, CLDIV, CLMUL, CLTOD, DTST, POWER, CDTOL, IDIV, UMOD
- It has utf8 conversion support on linux (probably on newer msys too).
- VGM logging

If anyone wants to contribute to it, the plan was to:

- make a better windows port
- test more programs with it and implement the missing DOS calls
- make more tests
- add a debugger (currently I debugged it by logging all the instructions to a file and comparing those to a working emulator)
- test with more music drivers
- compile a WASM binary and run it in the browser with mxdrv and pcm8a on my MDX database

Let me know if anyone finds this interesting and wants to contribute to it. The DOS calls are fairly easy to add, it's just a switch statement in v68doscall.c.

[vampirefrog]

Added a pre-release v0.1a to make it easy for windows folks.

[rezb1t]

This is really cool! I've been using run68x up to this point, but I think I will switch to this. I already made a quick port of v68 to macOS and it seems to be working!

I will clean up my changes and submit a pull request soon.

Thanks for sharing!