ZX48 DECA port

DECA top level by Somhic adapted from Kyp's ua2 port https://github.com/Kyp069/zx48 (video part from zxuno port).

See VGA or HDMI version in their respective folder.

VGA and HDMI versions differ in the following files: src/main.v, src/video.v, deca/zx48.qsf, deca/zx48.sv

Follows original readme.md.

zx48, a Sinclair ZX Spectrum 48K FPGA implementation

Supports this FPGA boards:

• ZX-Uno (http://zxuno.speccy.org/)
• ZXDOS and ZXDOS+ (https://www.antoniovillena.es/store/)
• MiST (https://github.com/mist-devel/mist-board/wiki)
• SiDi (https://manuferhi.com/p/sidi)
• UnAmiga Reloaded (https://github.com/UnAmigaReloaded-fpga)

Implements a standard ZX Spectrum 48K computer and the follwing hardware:

• DivMMC (esxdos 0.8.9)
• Specdrum
• Turbosound
• SA1099 (MiST, SiDi, UnAmiga)
• Joystick Kempston
• Tape loading

Keyboard shortcuts

• Spectrum Reset: F12 or Ctrl+Alt+Del (ZX-Uno, ZXDOS, ZXDOS+)
• Spectrum Reset: F6 or Ctrl+Alt+Del (MiST, SiDi, UnAmiga)
• FPGA Reset: F11 or Ctrl+Alt+Backspace (ZX-Uno, ZXDOS, ZXDOS+)
• NMI: F5
• Toggle RGB/VGA: scroll lock