A resilient LL Sparql parser.
This is supposed to become the core parser for the [Qlue-ls](https://github.com/IoannisNezis/Qlue-ls) Langauge server.
It uses [rowan](https://github.com/IoannisNezis/rowan) for the [red-green-tree](https://ericlippert.com/2012/06/08/red-green-trees/) datastructure under the hood.
The produced syntax trees are defined in [sparql.ungram](sparql.ungram).