Useful error messages, function parameters, and if/else/elseif/while statements fully work!

After quite a bit of code refactoring, all of the above work!
Nudl now tracks where in the source code a token is written for concise error messages. To make function parameters work, I had to change the generated code to use closures instead of functions in order for the parameters to work without explicit types.
Below is code with an intentional syntax error (on the right) and the error message in the console below. On the left is the generated Rust code (before I made the syntax error)