FAI REPL v0.4.3

Use the portable version if you have the .NET Core 2 runtime installed, and your platform-specific version otherwise. This version of FAI is relatively close to release quality. Most missing features involve extensibility of the language library, additional built-ins, and possible features like sets and matricies.

Note: Previous versions had an issue with text encoding on Unix. A UTF-16-capable terminal will handle those, but from now on only a UTF-8-capable terminal will be required (which Unix terminals generally support).