Merge pull request #24 from izaera/master

Remove Completers in favor on Future chaining so that code is cleaner and errors are not lost
mongo_dart_query published separately and added as dependency to mongo_dart. Unified SelectorBuilder will be used by mongo_dart and objectory.
v0.1.15
Update for changed SelectorBuilder
0.1.16
v0.1.17 Fix broken 0.1.16 pubspec