ERT-480: Added optional offset argument to point_fprintf().
ERT-480: Added tetrahedron_fprintf function.
ERT-480: Added NTG and MULTPV checks in grid volume checks.
ERT-480: Added method cell_regular.
ERT-480: Reformat slightly.
ERT-480: Added header for ecl_grid_regular1() functions.
ERT-480: Changed cell contains implementation to only consider simple planes for each cell.