v1.7.0 Multiple speed improvements

• Classification:
  • Significantly faster growing (two orders of magnitude for sets with >100k instances), faster pruning,
  • Added approximate mode (approximate_induction parameter). Note: this is an experimental feature - the results may change in future releases.
• Regression:
  • Mean-based growing set as default (few times faster then median, non-significant impact on accuracy).
• Survival:
  • Faster growing and pruning (few fold improvement).