Proposed HIR design

[Bill Cox]

A preliminary version can be found here.  Please feel free to give feedback.

The HIR, or "High-level Intermediate Representation" is a database of data structures used to represent Rune code by the bootstrap Rune compiler we're writing.  We may build an AST first, or maybe like the C Rune compiler, we'll parse directly into the HIR.

This is the most important part of the bootstrap Rune compiler to get right.  Doing it well will simplify the rest of the work on the compiler, and enable multiple folks to work somewhat independently on various parts of the compiler in parallel.

Bill