More optimization intended to reduce compile time. Another 10% speedup on compiling...

More optimization intended to reduce compile time. Another 10% speedup on compiling empty PEG parser
- new map-flat combinator replaces usages of 'map flatten' in compiler
- compiler.tree.def-use.simplified uses an explicit accumulator instead of flatten
- compiler.tree.tuple-unboxing uses an explicit accumulator instead of flatten
- fix inlining regression from last time: custom inlining results would sometimes be discarded
- compiler.tree's 3each and 3map combinators rewritten to not use flip
- rewrite math.partial-dispatch without locals (purely stylistic, no performance increase)
- hand-optimize flip for common arrays-of-arrays case
- don't run escape analysis and tuple unboxing if there are no allocations in the IR