Added a new geometrical data type: DOMAIN_INDEX.
Minor code reformatting.
Documented Geometry::getData().
Introduced the typedef Fiber::Function::ValueType.
Documented the members of Fiber::Function.
Improved documentation of SurfaceNormal(In)DependentFunction.
Added two new descendants of Fiber::Function, depending on domain indices.
Grid functions depending on domain index can be constructed from Python.