fixed count() bug
added: average(), sum()
disused `use` deleted
Changed so that `join` and `groupBy` might use `EqualityComparer`
Added `distinct` method
fixed #16 fixed #21
Renamed  bad param name
Renamed  class name `Delegate` to `Projection`
Removed constants Ginq::COUNTER, Ginq::VALUE_OF, Ginq::KEY_OF
Fixed PhpStorm code inspection warnings
Renamed ProjectionSelector, ProjectionJoinSelector, ProjectionPredicate to DelegateSelector, DelegateJoinSelector, DelegatePredicate
Changed EqualityComparer and Comparer method signature
Removed Ginq::seq()
Added `groupJoin`
Changed EqualityComparer and Comparer method signature
Changed testSelect()
Improved `repeat` method
Removed `find` `rest`
Added `first` `firstOrElse` `last` `lastOrElse` `aggregate` `elseIfZero`
Improved doc domments
Fixed assertEquals() calling parameters