Apparently some people feel that tree density is too thick in some biomes and would like to be able to reduce the amount of trees generated so forest are more sparse.

This should be configurable on a per-biome basis, so I'm thinking a tree density 'multiplier' for each biome should do the trick for now. Something like:

S:"Tree Density Multiplier"=1.0

and then in DecoTree we can multiply the local 'loops' variable by that value.

Yeah, I was thinking something along those lines. We'll need to set reasonable hard-coded upper limits though to prevent extreme values being set, because I can totally see people that don't know how the process works setting ridiculously high values and making the magic smoke leak out of their CPUs.

This is almost finished - just want to test a few more scenarios & then I'll submit a PR for review.

Added in 6dd8ade