Add release to changelog.

Merge pull request lyst#43 from maciejkula/prepare_release

Prepare 1.8 release.

Bump version to 1.7.

1.6 release.

1.5 release

Merge remote-tracking branch 'upstream/master'

Merge pull request lyst#14 from maciejkula/adadelta_squashed

Add adadelta learning schedule. Change init/fit API.

Bump version to 1.2.

Merge pull request lyst#12 from maciejkula/parallel_warp

Add parallel training for WARP and BPR losses.

Merge pull request lyst#11 from maciejkula/auc_test_fix

Fix AUC tests and example.