Terrain generator

Addition of inbuilt terrain generation code. Operates on the currently selected region.
Adds command
> terrain generate <type> <min height> <max height> [ smoothing ]

<type>  - Flatland (current default), Mainland (terrain generated to edge of region), Island (terrain surrounded by water)
< min height> <max height>  -  required minimum & maximum land heights
[smoothing] - options (default 2) - number of smoothing passes to perform