add SPARQL & Turtle highlighter

See https://www.w3.org/TR/sparql11-query/#sparqlGrammar
- http://rawgit2.com/VladimirAlexiev/grammar-diagrams/master/sparql11-grammar.ebnf for plain text version
- http://rawgit2.com/VladimirAlexiev/grammar-diagrams/master/sparql11-grammar.xhtml for railroad syntax diagrams.

I'm thinking of using this as a model:
https://github.com/jgm/skylighting/blob/master/skylighting-core/xml/sql.xml
@jgm, could you give me some pointers? I have a lot of questions (eg what is `#stay` and `#pop`, what is the list of reusable `itemDatas`...)

Guess I should first read https://docs.kde.org/stable5/en/applications/katepart/highlight.html,
then diff https://github.com/KDE/syntax-highlighting/blob/master/data/syntax/sql.xml to the above to see what changes skylighting has compared to KDE/syntax-highlighting?

My next question would be about Turtle: https://www.w3.org/TR/turtle/#h3_sec-grammar-grammar. It has very few keywords and relatively simple structure that consists mostly of terms.

Thanks for all your help!