Add coollang-2020-fs to Educational and Toy Projects

[mykolav]

coollang-2020-fs compiles a small but interesting Scala subset into x86-64 assembly.

• It compiles down to x86-64 assembly. Then invokes GNU as and ld to produce a native executable.
• The language is simple but not too simple. A lot of mini-compilers have languages with functions, primitive values and not much else. This project's language has classes, inheritance, virtual dispatch, and even a very simple form of pattern matching.
• The compiler is implemented in F#.