Support $text operator in query builder (fixes #162)

The $language option is supported via language(), which is similar to how $maxDistance is supported for geo-spatial operators.
Document var args for Builder exclude()/select()
Unit tests for Builder::sort()
Support $meta fields in query builder projections and sorts (fixes #152)
Remove redundant array initialization
Merge pull request #184 from doctrine/1.2-text-operator

Query builder support for $text operator in MongoDB 2.6