Add Xgboard working demo

Add MNIST benchmark on Deep Forest

Fix 2d MGScan + Add MNIST demo.

Fix early stopping in Cascade Forest

Add external model storage for Deep Forest.

Full rework of Deep Forest implementation.

Large metric fixes for Deep Forest.

Allow predicting Deep Forest from train, RF fix.

Fix Deep Forest examples library missing.

Change Deep Forest picture (wrong one)

Add Deep Forest implementation.

Fix hardcoded values in partial dependence.

Add Partial Dependency Analysis and dependencies.

data.table>=1.10.4 has fwrite (issue #5)

Add new ML model: Dynamic Boosted Trees