Merge pull request #157 from slayoo/master

moving shallow_water solver from thests to the library tree; libmpdata++-config.cmake
adapt 3d pressure solver to API changes
make xdmf_writer work with boost >= 1.56 and fix off by one error
do not make real_t private in pressure solvers
adding outwindow output option for output at consecutive timesteps
adding initial version of the new solver with subgrid terms
adding basic Taylor-Green vortex test