Add copyright notice and license.
Add constructors and toString methods.
Add parser.
Move JS to scripts directory.
Import Underscore.js.

Underscore.js 1.6.0
Refactor ast and parser.

Change AST.Var type to a string.
Remove JSlint annotations.

JSlint has become more trouble than it's worth on this project.
Add normal-order interpreter.

This is a substitutional interpreter. It has really bad performance as program
size grows. It will eventually need to be replaced by an "eval/apply"-style
interpreter, or something else.