AnvilStats: initial per-height blocktype implementation (WIP).
AnvilStats: Fixed Win64 compilation.
AnvilStats: Added cmake directive for larger executable stack.

This fixes runtime "stack overflow" errors caused by large stack-allocated arrays used for decompression.
AnvilStats: Ignoring output XLS files.
AnvilStats: Added per-height spawner stats.
AnvilStats: Fixed thread start race condition.

The whole program would sometimes fail to process anything because the threads were waited-for before they were started.
Merge pull request #1346 from mc-server/AnvilStatsHeights

Anvil stats heights