add `geoYAMLLiteral`

[VladimirAlexiev]

geo:geoJSONLiteral is the way to store GeoJSON data in RDF.
But YAML is much nicer than JSON: it's a superset of JSON, but also includes much easier to read structures based on identation not punctuation.

I googled "geojson yaml" and surely, I got https://github.com/louh/geoyaml.

YAML-LD was defined as a W3C spec maybe 2-3 years ago, and got some traction.

• Serializing JSON or YAML literal in YAML-LD w3c/yaml-ld#36 : If this issue is accepted, we can have YAML-LD data that carries GeoYAML literals.

Then we need datatype ^^geo:geoYAMLLiteral.
But it could use the existing prop geo:asGeoJSON because it's a syntactic variant of the same serialization.

[nicholascar]

We're creating a register of data types that can site outside the core standard but define all the predicates and datatypes needed for lots of other formats. Implementers can then list the ones they support.

There are so many formats that are useful for different purposes, such as 3D, ease of reading etc., that we want a dynamic register that can be added to more quickly than new standard versions can be made.