Landclass information is typically not high enough resolution
to render small beaches and coastline features.
This commit uses the steepness of the elevation mesh
to procedurally generate:
a) sea-cliffs (poorly - just a texture at present)
b) beaches, which mix into translucent shallow water
c) breaking waves (poorly - uses the wind direction rather than the
slope normal)
Previously the water shader was separate and executed on a
different mesh.
This adds the water shader as a separate fragment function
(ws30-water.frag) and uses a material parameter passed in
as a Uniform to use it in preference to the usual texel
lookup.
Performance testing found a slight performance improvement
from having a single mesh, but a slight performance impact
from the extra fragment shader complexity.
