Emscripten: support 3 javascript emulators (SAE, EM-DOSBOX, JSMESS)

[haschimoto]

Emularity has those 3 emulators covered for easy embed: https://github.com/db48x/emularity

• SAE (Javascript of WinUAE): https://github.com/naTmeg/ScriptedAmigaEmulator

• EM-DOSBOX (EM-Scripten of Dosbox): https://github.com/dreamlayers/em-dosbox/

• JSMESS (Javascript of MAME) https://github.com/jsmess/jsmess/blob/master/README.md now part of MAME, read: http://docs.mamedev.org/initialsetup/compilingmame.html#emscripten-javascript-and-html

Other tech used: https://github.com/jvilk/BrowserFS https://github.com/stefanpenner/es6-promise

[haschimoto]

Jsdosbox example: https://proxy1.zn.kindlyfire.me/13ozLST1c4rqUjCNLg1YFGWnYVVfPsVqnV/

[haschimoto]

nice emscripten presentation: https://kripken.github.io/mloc_emscripten_talk/cppcon.html#/