Eve-elastic

++++++++++++++++

- allow list of urls to be set in ``ELASTICSEARCH_URL``
- add support for ``where`` param
- handle ``bson.ObjectId`` serialization

++++++++++++++++++

- fix ``init_index`` on versions endpoints

++++++++++++++++

- implement ``elastic_prefix`` resource config similar to ``mongo_prefix`` in eve
- change ``init_app`` behaviour - it won't call ``init_index`` anymore, it must be
called explicitly

++++++++++++++++++

- add search highlights config
- fix aggregations request trigger parsing

++++++++++++++++++

- fix search when there is no ``request.args``

++++++++++++++++++

- fix ``find_one`` with multi term lookup