Isolate Femtolisp global state and import many patches from Julia

[DemiMarie]

This imports many patches from Julia’s fork of Femtolisp. The main one, and the reason for the effort, is removing all global state from the Femtolisp VM. However, there are several others, including:

• immediately-invoked lambda expressions don’t allocate a closure
• a memory-debugging mode with Valgrind support
• C implementations of more builtins

I used Emacs’s diff mode to apply the (rather large) patch set, since it could not be applied automatically (this would wipe out many features that Julia’s fork doesn’t have).