New O(log(word size)) code for Z curve intersection with hyperbox

 * Profiling indicates around a 4x speedup
 * Further speedup possible with bit intrinsics
New O(log(word size)) code for X, Y to Z value computation

 * Profiling indicates around a 1.75x speedup
Rewrite the individual code to use flat arrays

 * Profiling indicates around a 1.5x speedup
Model from Caplat and Anand's Journal of Ecology 2009 paper
Track simulation time and total individuals
Missing growth decay constant provided by Paul
Vary regions linear with height instead of constant

 * Changes results and greatly decreases simulation time due to
   ending most inter-sapling competition