Added link_at_face function.
Added link_at_face function.

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