Merge pull request #16 from lukechampine/ast

AST reorganization
use Value instead of Value*
use ASTnode instead of ASTnode*
free environments
Valgrind #1: free arglist
remove memcpy
Valgrind #2: free import strings
can't use NULL anymore
clean up some silliness
Merge pull request #17 from lukechampine/import

Add support for importing existing scripts
allocate environments on stack
tweak assignOp() and chain()
Merge branch 'master' of github.com:mkvsynth/mkvsynth
remove unnecessary free()
initialize nodes with {}
Merge pull request #22 from lukechampine/memory

Memory management