Kaleidoscope

Implementation of Kaleidoscope language in Swift.

See https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/index.html

List of potential improvements:

• Make Codegen.expr switch over enum rather than types.
• Visitor pattern?
• Make compiler work over static files rather than REPL only.
• Cover with tests at least parsing part.
  • How to cover codegen?
• Is it possible to use LLVM directly (without C wrapper) with latest Swift interop?