The dune-grid-glue module provides infrastructure for the coupling of two
unrelated Dune grids. The coupling may be overlapping or nonoverlapping,
conforming or nonconforming. The two grids are not requested to be of the same
type, and they may even be of different dimensions.

Couplings are described as sets of remote intersections. Conceptually, these
remote intersections are very close to what the regular intersections in the
Dune grid interface are, with the difference that the inside and outside
entities are taken from different grids.