New and Spawn built in functions

Added `new` and `spawn` to the set of built in functions allowing you to
get instances of classes.

There are a number of bugs here:

* Object.Spawn.call (line 61) looks in the instance vars for methods.
  This should be a simple fix except that it messes with Boot's load
  sequence in some odd ways
* Scoped searches do the wrong thing when they fail to find the vlaue they
  are looking for.  (See Context.hs:93)

Todo:

* reopen a class
* REPL to load a file