Properties for radial grids
Properties for radial grids

Added a bunch of radial-specific properties to the radial grid, to
enhance usability. Can now interrogate:
- number_of_shells
- shell_spacing
- number_of_nodes_in_shell
- radius_to_shell
- radius_at_node

ManuSchmi88/landlab,SiccarPoint/landlab,landlab/landlab,amandersillinois/landlab,laijingtao/landlab,ManuSchmi88/landlab,RondaStrauch/landlab,cmshobe/landlab,Carralex/landlab,cmshobe/landlab,Carralex/landlab,Carralex/landlab,laijingtao/landlab,landlab/landlab,RondaStrauch/landlab,csherwood-usgs/landlab,csherwood-usgs/landlab,ManuSchmi88/landlab,RondaStrauch/landlab,amandersillinois/landlab,cmshobe/landlab,landlab/landlab,SiccarPoint/landlab