Previously, smooth materials would get extra triangles at the top to create
slopes instead of steps. Now those also appear at the bottom.
Smooth also gets generally smoother at the bottom, while Rough gets rougher
at the top. The new Smoother material is somewhere between Flat and Smooth.
Octagon is like Flat but also gets straight slope triangles.
+ Refactored the ShakeFree, BlastFree, DigFree, DrawQuad etc. functions and
removed unused functions ClearRectDensity, DigFreeMaterial,...
+ Moved the polygon fill algorithm from StdSurface8.cpp to C4Landscape.cpp
+ Clearance functions which used to subtract a circle now subtract something
that looks more like a chunk
+ Pickaxe works with BlastFree now
+ Removed Dig2ObjectRequest