Merge pull request #1 from roberthannon/master

Added support for operator field option
Operators now take ICollection instead of IEnumberable.

Guards against possible multiple enumeration of IEnumerable.
Merge pull request #3 from roberthannon/master

Added support for return fields and improved expression support
Prep for 0.6 release.
Merge pull request #4 from roberthannon/master

Added support for filter queries
Prep for 0.7 release.