Types (Structs)

Need to be able to support user defined types.

```lisp
:: Type definition
(type 'person '[name age])

:: Instantiation
(set 'pebaz (new person "Pebaz" 24))

:: Usage
(print (get pebaz 'name))
(print (get pebaz "name"))

:: Future
(print pebaz/name)
```

Once the #29 Dict type is created, it will be easy to make `type` definitions return `Dict`s.
