Implemented a pattern based peephole optimizer.

Implemented a pattern based peephole optimizer.

Main improvements:

 1. every CONS-[MULTI]CLOSURE saves one instruction
 2. most funcalls save one stack access
 3. fixnum arithmetic (plus and minus constants)
 4. fixnum case of generic add/subtract constant
 5. fixnum bitwise operations with constants (and/or/not)

1 and 2 give about 5% on closure/funcall heavy code.

3-5 are improvements made possible by the screwy fixnum tag.
`Natural' fixnum tags would make them obsolete (but some of the
rewrites are as good). 5 improves hash table operations up to 10% due
to how `flags' are implemented.