Support wildcards and regexp queries

[dennwc]

Implement a subset of regexp - a wildcard query (LIKE in SQL). Resolves #664.

At the same time enable regexp optimization for all backends.

Wildcards are exposed in path lib:

p.HasFilter(quad.IRI("name"), false, shape.Wildcard{
  Pattern: `An%`,
})

And in Gizmo:

g.V().Has("<name>", like("An%"))