Features
* Initial classes for `RasHdf`, `RasGeomHdf`, `RasPlanHdf` as subclasses of `h5py.File`
* Methods implemented:
* `projection`: return the projection as a pyproj `CRS` object
* `mesh_area_names`: return the list of 2D mesh area names
* Methods returning `GeoDataFrame` objects:
* `mesh_areas`: 2D flow area perimeter polygons
* `mesh_cell_polygons`: 2D flow area cells as polygons
* `mesh_cell_points`: 2D flow area cell centers
* `mesh_cell_faces`: 2D flow area cell faces as lines