Log Message:
emulators: add gearboy

Gearboy is a cross-platform Game Boy / GameBoy Color emulator written in C++.

## Features

- Accurate CPU emulation, passes cpu_instrs.gb from blargg's tests.
- Accurate instruction and memory timing, passes instr_timing.gb and
  mem_timing.gb from blargg's tests.
- Supported cartridges: ROM, ROM + RAM, MBC1, MBC2, MBC3 + RTC, MBC5, HuC-1
  and MBC1M (multicart).
- Accurate LCD controller emulation with correct timings and priorities
  including mid-scanline effects.
- Game Boy Color support.
- LCD screen ghosting effect as seen in the original Game Boy.
- LCD dot matrix effect.
- Sound emulation using SDL Audio and Gb_Snd_Emu library.
- Save battery powered RAM cartridges to file.
- Save states.
- Compressed rom support (ZIP).
- Game Genie and GameShark cheat support.
- Full debugger with disassembler, breakpoints, debug symbols, memory editor,
  IO inspector and and VRAM viewer including tiles, sprites, backgrounds and
  palettes.