[MRG] multilabel accuracywith jaccard the index

This pr intends to bring multilabel accuracy and zero-one loss based on the jaccard index.

For reference, see section 7.1.1 of [Mining Multi-label Data](http://lkm.fri.uni-lj.si/xaigor/slo/pedagosko/dr-ui/tsoumakas09-dmkdh.pdf) and the [Wikipedia entry on Jaccard index](http://en.wikipedia.org/wiki/Jaccard_index).

TODO list:
- [x] Add multilabel accuracy based on jaccard similarity score
- [x] write narrative doc for accuracy based on jaccard similarity score
- [x] Update what's new?

This was removed of the pr scope:
- Add multilabel zero-one loss based on jaccard distance
- write narrative doc for multilabel zero-one loss based on jaccard distance