[eval2] Begin transformation into a pseudo-bytecode compiler.
[eval2] LET: Implement dynamic binding correctly.
[eval2] Reimplement LET*, fix LET.
[eval2] Various fixes and improvements.
[eval2] Reimplement FLET, LABELS.
[eval2] Reimplement BLOCK, RETURN-FROM, TAGBODY, GO, MULTIPLE-VALUE-BIND.