There's no benefit to using C include guards so switch to pragma once
everywhere for consistency.
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Also replace derived types (map_type, collection_type, etc.).
As we'll change data_type's definition, this reduces the number of places
that need to be modified later, and is more readable.
The Functions class wants to store functions in a map and hand them out later,
so we need a shared_ptr.
(could have had a map of name -> function factory, maybe one day)
