Added get_area_of_patch function.
Added get_area_of_patch function.

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