evaluate Qlever as a fast, alternate sparql engine

[mbjones]

Qlever: https://github.com/ad-freiburg/qlever

Advertised as a fast query engine:

QLever (pronounced "Clever") is a SPARQL engine that can efficiently index and query very large knowledge graphs with over 100 billion triples on a single standard PC or server. In particular, QLever is fast for queries that involve large intermediate or final results, which are notoriously hard for engines like Blazegraph or Virtuoso. QLever also supports search in text associated with the knowledge base, as well as SPARQL autocompletion.