Initial port of compiler

[ahejlsberg]

Initial port of TypeScript compiler to Go. Currently includes scanner, parser, binder, and beginnings of program construction and checker. For now, very simple project model: All files must be under a common root and program consists of all .ts or .tsx files under that root. No tsconfig.json support yet.

Build and then run on the .ts and .tsx files in a directory

tsgo tscomp

By default this parses and binds all .ts and .tsx files in the directory and then performs a simplified type checking pass that
just resolves identifiers in expression positions. Use -p flag to only parse and bind and skip the check pass. Use -s flag
to parse and bind on a single thread (instead of in parallel on multiple threads). Use -q flag to suppress output of diagnostics.

Lots more to come...