add random number generator helper extension methods
minor vertex count calculation fixes in GeometryDebugRenderer
add convenience overload
add extra bit helper methods for setting/getting smaller integer-type values in bitfields
rename to Bits since some methods are now not just extension methods

Easier to type 'Bits' :)
add Clear()
add TileContainer Get/GetSafe overloads accepting a Point3
fix bit int-value setting to properly overwrite all the bits instead of only OR-ing them in