Lower to 1G JVMs for windows

Unwind if this breaks linux & the windows user will suffer
emacs proj file updates
Enable flow-coding
Enable parallel single-tree-growing

Means can build splits in parallel on 1 tree (not just building trees in
parallel)
Parallelize tree-building better

Fully parallel per K-trees, including the per-level decision making.
Also more per-tree error reporting; throttle scoring after a few
seconds.