Cleaned up get_angle_of_link, added doctests.
Cleaned up get_angle_of_link, added doctests.

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