Minor change to hillslope_ca.py
Minor change to link_ca.py
Merge branch 'master' of https://github.com/landlab/landlab

Conflicts:
	landlab/components/linkca/examples/hillslope_ca.py
Generalizing Landlab's CA

We now have:
- a base class, LandlabCellularAutomaton (LCA for short), that
implements a generic form of a continuous-time stochastic CA
- a derived class, RasterLCA, that represents a simple, non-oriented,
raster-based LCA. The behavior of this and the base class should be
identical
- a new version of the weathering CA, called saprolite_weathering, that
illustrates the capability of a RasterLCA
- more derived classes to come ...