bugfix: lambda must use new_scope to gen body code
[xhash] fix a bug in xh_destroy
add -g option to the build command line
rename pic_scope -> codegen_scope
evaluate arguments in normal (lexical) order
introduce codegen_state structure
cleanup codegen.c
fix a memory bug in xhash
throw wrong number of arguments error for user defined lambda call
add pic_calloc
test implementation for closed variable reference
add pic_env struct
add OP_CREF
initial closure support
add OP_LSET and OP_CSET