Log Message:
emulators: add gearsystem

Gearsystem is a cross-platform Sega Master System / Game Gear / SG-1000
emulator written in C++.

## Features

- Accurate Z80 core, including undocumented opcodes and behaviour like R
  and MEMPTR registers.
- Multi-Mapper support: SEGA, Codemasters, Korean, MSX, SG-1000, and ROM
  only cartridges.
- External RAM support with save files.
- Automatic region detection: NTSC-JAP, NTSC-USA, PAL-EUR.
- Accurate VDP emulation including timing and SMS2 only 224 mode support.
- Internal database for rom detection.
- Audio emulation using SDL Audio and Sms_Snd_Emu library.
- Saves battery powered RAM cartridges to file.
- Save states.
- Compressed rom support (ZIP deflate).
- Game Genie and Pro Action Replay cheat support.
- Full debugger with disassembler, breakpoints, debug symbols, memory editor,
  IO inspector and and VRAM viewer including tiles, sprites, backgrounds and
  palettes.