General Il traversal

[matijapretnar]

When I started writing my own IL pass, I noticed how much boilerplate there is in the traversal. This tries to resolve the problem by creating a generic function that traverses the whole script, with hooks in the proper places. I will make a PR when I am able to succinctly express all current passes written by @nomeata, but I still wanted to show you where things are heading right now.

[nomeata]

I welcome nice helpers for common cases, although i wondering how often one needs to write a pass that doesn't fit this scheme (local env updates, different accumulators in different surpasses etc.)

Personally I'd probably lean towards simplifying the structure of the AST so that there is less boiler plate code to write (E.g. BinOp and RelOp really don't need to be different at this point).

But this is not to discourage you; if indeed it removes the boiler plate code from most passes then great!