Explore potentially splitting parsing and binding

[SPGoding]

The parser is responsible for both producing the AST and inserting symbols into the symbol table at the moment. By separating the parsing and binding process, we can eliminate side effects of parsers and run parsers for different files concurrently using web workers (on browser) / worker threads (on Node.js).

Potential libraries we could use:

• https://github.com/josdejong/workerpool
• https://github.com/andywer/threads.js

[misode]

@SPGoding Has this issue not been completed already? Or would you want to actually do the concurrent parsing?