Release 0.3.0

[glemaitre]

TODO:

• Merge [MRG] EHN handling sparse matrices whenever possible #316

• Merge Allows ClusterCentroids for hard and soft voting #317

• Merge [MRG] EHN add BalancedBaggingClassifier #315

• Create 0.3.X branch

• Update gh-pages and the stable version to point on 0.3

• Create a release with tag

• Upload pypi/conda packages.

• Try conda-forge again.

• bumpversion to 0.4.0.dev0

[glemaitre]

@massich @chkoar I am going to make the release not later than Thursday.
If you can review the PR above. Otherwise, I will merge it anyway :)

[massich]

@glemaitre can you rebase the PRs before review? Thx

[massich]

well... its seems there are no more PR related !!! (Push the green button)
cc: @scikit-learn-contrib/imbalanced-learn