Add execution option to Elastica\Filter\Range
Update test for Elastica\Filter\Range::toArray

Tested example was deprecated since ES 0.90.4
Add missing constant to Elastica\Filter\GeoDistance

From http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-geo-distance-filter.html#_options_4
Add existence/null_value options to Elastica\Filter\Missing
Add min_children/max_children options to Elastica\Filter\HasChild
Update Elastica\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 Elastica\Filter\Terms
Improve coverage