libctf: core type lookup

libctf: core type lookup

Finally we get to the functions used to actually look up and enumerate
properties of types in a container (names, sizes, members, what type a
pointer or cv-qual references, determination of whether two types are
assignment-compatible, etc).

With a very few exceptions these do not work for types newly added via
ctf_add_*(): they only work on types in read-only containers, or types
added before the most recent call to ctf_update().

This also adds support for lookup of "variables" (string -> type ID
mappings) and for generation of C type names corresponding to a type ID.

libctf/
	* ctf-decl.c: New file.
	* ctf-types.c: Likewise.
	* ctf-impl.h: New declarations.

include/
	* ctf-api.h (ctf_visit_f): New definition.
	(ctf_member_f): Likewise.
	(ctf_enum_f): Likewise.
	(ctf_variable_f): Likewise.
	(ctf_type_f): Likewise.
	(ctf_type_isparent): Likewise.
	(ctf_type_ischild): Likewise.
	(ctf_type_resolve): Likewise.
	(ctf_type_aname): Likewise.
	(ctf_type_lname): Likewise.
	(ctf_type_name): Likewise.
	(ctf_type_sizee): Likewise.
	(ctf_type_align): Likewise.
	(ctf_type_kind): Likewise.
	(ctf_type_reference): Likewise.
	(ctf_type_pointer): Likewise.
	(ctf_type_encoding): Likewise.
	(ctf_type_visit): Likewise.
	(ctf_type_cmp): Likewise.
	(ctf_type_compat): Likewise.
	(ctf_member_info): Likewise.
	(ctf_array_info): Likewise.
	(ctf_enum_name): Likewise.
	(ctf_enum_value): Likewise.
	(ctf_member_iter): Likewise.
	(ctf_enum_iter): Likewise.
	(ctf_type_iter): Likewise.
	(ctf_variable_iter): Likewise.