libctf: debug dumping

libctf: debug dumping

This introduces ctf_dump(), an iterator which returns a series of
strings, each representing a debugging dump of one item from a given
section in the CTF file.  The items may be multiline: a callback is
provided to allow the caller to decorate each line as they desire before
the line is returned.

libctf/
	* ctf-dump.c: New.

include/
	* ctf-api.h (ctf_dump_decorate_f): New.
	(ctf_dump_state_t): new.
	(ctf_dump): New.