* Added calculate_max_gradient_across_adjacent_cells method to RasterModelGrid.
* Added calculate_max_gradient_across_adjacent_cells method to RasterModelGrid.

== Added ==

* calculate_max_gradient_across_adjacent_cells method is intended to replace
  RasterModelGrid methods:
  - find_node_in_direction_of_max_slope
  - find_node_in_direction_of_max_slope_d4



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