command line interface

This is the beginning of the command line interface, based on the parser we created a few months ago.

Example usage, in the JavaScript console in cli/index.html:

```javascript
var e1 = new E3.Vec(1, 0, 0); // unit vector
var e2 = new E3.Vec(0, 1, 0); // unit vector
var e12 = run("e1^e2");       // parses and runs ga code
```

A next step is adding assignment, line breaks and object creation to the language to enable simple scripts like this:

```
e1 = vec(1,0,0)
e2 = vec(0,0,0)
e12 = e1^e2
```