dump: replace C implementation with simpler Lua dump.

* specs/ext_lyaml_emitter_spec.yaml: Specify low level libYAML
emitter binding.
* specs/spec_helper.lua (emitevents, emit): New helper functions.
* specs/specs.mk (specl_SPECS): Add
specs/ext_lyaml_emitter_spec.yaml.
* ext/lyaml/lyaml.h: Factor common macros and headers into this
single file.
* ext/lyaml/parser.c, ext/lyaml/scanner.c: Adjust accordingly.
* ext/lyaml/lyaml.c (lua_yaml_dumper, dump_node, dump_scalar)
(get_yaml_anchor, dump_table, dump_array, figure_table_type)
(dump_null, dump_node, dump_document, append_output)
(find_references, Pdump): Remove.
* ext/lyaml/emitter.c: New file, implementing libYAML emitter
binding.
* lib/lyaml.lua (M.dump): Reimplement dumper in Lua.
* local.mk (ext_lyaml_lyaml_la_SOURCES): Add ext/lyaml/emitter.c.
(EXTRA_DIST): Add ext/lyaml/lyaml.h.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
maint: maintain API backwards compatibility with legacy C implementation.

Make sure the old lyaml.load and lyaml.dump APIs work by switching
the naming of the C and lua parts of the new implementation.
* ext/lyaml: Rename from this...
* ext/yaml: ...to this.
* ext/lyaml/lyaml.c: Rename from this...
* ext/lyaml/yaml.c: ...to this.
* lib/yaml.lua: Rename from this...
* lib/lyaml.lua: ...to this.
* specs/ext_lyaml_emitter_spec.yaml,
specs/ext_lyaml_parser_spec.yaml,
specs/ext_lyaml_scanner_spec.yaml, specs/lib_yaml_spec.yaml:
Rename from these...
* specs/ext_yaml_emitter_spec.yaml,
specs/ext_yaml_parser_spec.yaml,
specs/ext_yaml_scanner_spec.yaml, specs/lib_lyaml_spec.yaml:
...to these.
* local.mk, specs/specs.mk, specs/spec_helper.lua: Adjust.
* NEWS: Remove all the incompatibility warnings, and adjust.

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