lyaml: bind lyaml.parser to lyaml_parser_parse.

* configure.ac: Require Specl.
(SPECL_MIN): Require at least release 8 of Specl.
* specs/parser_spec.yaml: Specify behaviour of new parser API.
* specs/spec_helper.lua: New file. Specl helper functions.
* specs/specs.mk: New file. Run specl checks, and distribute
spec files.
* local.mk: Include it.
(lyaml_cpath): Factored out of MKROCKSPECS_ENV.
(MKROCKSPECS_ENV, LUA_ENV): Adjust.
* parser.c (Pparser): New file. Implement event iterator.
* lyaml.c: Include it.
(R): Add Pparser.
(luaopen_lyaml): Set up _gc metatable for iterator to clean
up iterator memory.
* local.mk (EXTRA_DIST): Add parser.c.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>