Adds:
- ast/Argument: AST node for an argument passed to a function.
- ast/FunctionCall: AST node for a function call.
- codegen/ModuleDeclarationRegistrar: The code generator registers module function declarations with this in order to determine module indexes and function indexes for instructions.
- model/FunctionLink: this is a reference either:
- from: a FunctionCall or a FunctionReference
- to: a ModuleFunctionDeclaration or a UserFunction
- optimizer/ReferencedFunctionGatherer: a visitor that determines which module functions and user functions are referenced, by looking at function calls and function references.
Also:
- CodeGenerator registers module functions
- InstructionGenerator generates code for function calls
- InstructionEmitter generates TOK_FUNC instructions
- StoredTokenDecoder decodes TOK_FUNC instructions
After all of this, the compiler can compile print("hello, world");
