Can now be used in the pure cmake as well as in the autotools/cmake
situation. In the end GRIDDIM and GRIDTYPE are define as cached variables.

now that it actually gets compiled...

dune_add_library apparently DOES NOT add all_pkg_flags to the compile,
because ofc it doesn't

This fixes some warnings in 'VectorType vec(size_t)' when VectorType was a
FieldVector< int, ... > bc. of the size_t to int conversion and is a more
general solution in general.

This adds the possibility to convert 'true' and 'false' together with their
uppercase variants to bool. This allows to use an ini file with dune and
python (as it used to be). Fixes #12