Finally allow for static hashes. Fixes GH #2.

This introduces a new token, tk_arrow (=>), to handle showing the associativity
between the key and the value. tree_hash, also introduced, holds a chain of
key, value, key, value, ... pairs which is looked over when building a hash.

Hash building accounts for multiple keys, and makes the right-most key the
resulting value. This is what Python and Ruby do (as well as Lua, I think). Keys
and values do not default to object just yet. For keys, this was intentional
(objects cannot be keys). For objects, this is due to a decision to stall that
off until a bit later.

Added some tests to sanity.ly to test the new static hash creation.