Additional get() and operator() for GhostLayerFieldAdaptor

See merge request walberla/walberla!135

Interpolator fix

See merge request walberla/walberla!134

added filter to exclude external libraries

use modern c++

See merge request walberla/walberla!130

Resolve "JSON output for timing"

Closes #65

See merge request walberla/walberla!127

Enable raytracing of ConvexPolygon pe body

See merge request walberla/walberla!131

Fix pe::findContainingProcess for bodies within -1*epsilon of a block edge

See merge request walberla/walberla!128

pe_coupling geometry: squirmers are spheres too

See merge request walberla/walberla!129

The necessary to_json(...) function are used. One can create a json
object by e.g. "nlohmann::json ttjson = nlohmann::json(tt)" with tt
being a timing tree