Library function return & param types (primitives-config)

[kaisucode]

Right now, the prototype for method calls' return and parameters types rely on primitives-config.js file, borrowed from the wescheme-blocks project. This should be tailored to support Pyret's library methods and their return/parameter types (and number of parameters) instead.

In addition, currently the type validation from the file is done by referring to a constant in PyretParser.ts named FIXED_SIZE_DATATYPES, but that should be expanded in the future to take other, non-fixed size datatype names as well. All unrecognized types are classified as "untyped" and still rendered.