Syntax for datatypes.

[timothee-haudebourg]

There is currently no way of defining datatypes within TreeLDR. The only datatypes are the one built in the compiler (for now, just xsd:string). This is so fundamental we need to add a syntactic construct for them.

Since there is already the type keyword, I propose to add datatype keyword. This keyword would behave just like type, but creating an instance of rdfs:Datatype instead of rdfs:Class. Then the with keyword can still be used to define its associated layout.

datatype xsd:integer with tldr:Integer;