GitLab

Changes include:

- The "Library" menu was replaced with the "Systems" menu
- The "Settings" menu was reorganised
- Game Boy rumble is now under the MBC5 "controller" for the cartridge "port",
  instead of being presented as a part of the base console
- Import instructions now mention that icarus ships with some firmware files,
  and describe the "Firmware" directory that icarus will use for firmware
  it needs.
- Apparently the correct name is "MSU1", not "MSU-1"
- v107 changes the way MSU1 data is stored in game folders
- PowerFest '94 import instructions removed, since I can't get it to work
  with v107
- Links to the official forum have been replaced with links to the unofficial
  forum archive, since the official forum is shutting down
- Links to Mercurial Magic updated to point at qwertymodo's archive, since
  hex_usr is no longer developing it
- Links to nSide updated, since hex_usr no longer uses GitHub.
- Windows build instructions now describe a compiler that is actually
  maintained, instead of stale TDM64-GCC.
- Linux build instructions now mention higan requires SDL 2.0.
- minor wording changes, typos, broken links fixed, etc.

Changes include a few typos, a few capitalization changes, and a lot of hyphenation of compound words that were not as widely used as I thought.

Since higan does not follow the conventional git development model,
we should prominently document how people can contribute.