Added node_types param to sitedef_parser.

Removed the corresponding node_types field from struct sitedef_parse_state.
Added node_types parameter to alloc functions for sitedef lexer and parser.

Added opaque typedef "parse_node_types_t" for sitedef_node_types.
Added a parse_node_types_t field to sitedef_node and changed the
sitedef_node_alloc_description() function to use it.

The sitedef_node package is now nearly decoupled from sitedef_node_types.