input heightmap range scaling

If the input heightmap has heights greater than 255, it can't fit in the game. There should be several options for how to deal with this:
- No scaling (clipping)
- Linear scaling
- Logarithmic scaling

Start by tracing how input heightmap heights above 255 are converted before being written into the Minecraft world. Determine where the scaling choice belongs and how the existing height range is handled. Done means the input supports no scaling with clipping, linear scaling, and logarithmic scaling, with each option producing a valid game heightmap.

Written by the indexing model from the issue text.