Override functions / methods

[tshort]

It'd be nice to override methods and functions. For example, I've been adding functionality over the last week, but it's running less code, because I'm pushing deeper into call trees.

A main culprit right now is throw. If that could be replaced with something simpler, more code would run. (String code doesn't work very well right now.)

You can already do this for some cases. If you "precompile" a method into a CodeCtx, codegen! will use that method when called.

It might be nice to have more general overrides. For example, I might want to overload all of the throw methods.