Added unravel function.
Added unravel function.

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