Make categorize() just work on atoms and get called during parenthesize().

* Only applied to atoms, so its weird it had to know how to traverse array.
Make built-in fn invocation run off JS functions.

* No longer insert special node into AST.
* Identifier lookup becomes just a context lookup.
* When figuring out if a list is an invocation, just check if first element is a JS function.
Make lambda definition just a JS fn.

* Compatible with new regime where invocation code just checks to see if first element of list is a JS function.
Remove lambda test that checks for old lambda AST node.
Complete renaming to Little Lisp.
Remove repl run shortcut that is longer than longcut.