Prepare for v0.5.0 release.

Merge pull request #32 from maciejkula/fix/serialization

Fix EncodableRng JSON serialization.

Merge pull request #30 from maciejkula/remove_unused_import

Remove unused import in decision_tree.rs

Merge pull request #25 from maciejkula/parallel_predict

Parallel model fitting and prediction

Merge pull request #20 from maciejkula/bump_bincode

Bump bincode to fix upstream breakage.

Version 0.2.0