changed depth to topo in topotools for clarity
changed bathy to topo for clarity
changed 'project' to 'interp' for clarity since it's really interpolation onto a grid not projection that is done for unstructured grids
Modified Topography class so that __init__ does not require path and read has several new arguments to allow specifying path, topo_type,  unstructured when calling the read method.
Fixed several bugs in Topography and perhaps fixed crop method, but not yet completely tested.  See RJL: comments for concerns