Add missing constant to Filter\GeoDistance
Add existence/null_value options to Filter\Missing
Add min_children/max_children options to Filter\HasChild
Update Filter\Indices

- New method addIndex allow to add indices one by one
- Indices may be specified by passing an instance of Elastica\Index instead of name string
Add execution option to Filter\Terms
Improve coverage
Remove Filter\Bool::setBoost

This function actually doesn't nothing:
- Boost parameter is for queries, not filters
- Even so, $boolFilter->setBoost(1.5)->toArray() returns array without "boost" key
Update Filter\Nested

- Remove setScoreMode, because this option is for nested query, not nested filter
- Add join option
Update Filter\HasParent

- _scope parameter was removed since ES 0.9
- Parent type can be specified by passing an instance of Elastica\Type
- Rewrite HasParentTest to use setUp/tearDown
Update Filter\HasChild

- _scope parameter was removed since ES 0.9
- Child type can be specified by passing an instance of Elastica\Type
- Rewrite HasChildTest to use setUp/tearDown
Better coverage
Update changes.txt