Post higan architecture docs to the wiki

[Screwtapello]

When byuu gave me a backup of the contents of byuu.org, it included two articles about higan's architecture: one about the Emulator::Interface API that the front-ends use to talk to higan's emulation cores, and one about the higan::Platform API that the cores use to talk to the outside world - find and load files, emit video and audio data, etc.

These will be very important for anybody working on higan or writing a front-end, but I think they fit better in the higan repo itself, or on the wiki, rather than on byuu.org.

[merryhime]

Preferrably in the repo itself:

1. Can be updated alongside the interface itself. (The wiki has a separate github repo as a backend.)
2. Doesn't rely on GitHub exisitng.