Hit detect circle points with no fill
Merge pull request #1595 from elemoine/icon-hit-detection

Hit detect circle points with no fill
allow target to be specified as a string for controls, update the documentation to make more clear what element and target are for
simplify the assignment of this.target_
remove question mark since all object properties are nullable by default
Merge pull request #1220 from bartvde/control-target

shouldn't we allow to pass in target as string as well for controls? (r=@elemoine,@ahocevar)
Convert ol.CollectionEvent#getElement method into element property
Convert ol.interaction.DragAndDropEvent#get* methods into properties
Convert ol.ObjectEvent#getKey method into key property
Convert ol.render.Event#get* methods into properties
Convert ol.source.VectorEvent#getFeature method into feature property
Convert ol.DrawEvent#getFeature method into feature property
Convert ol.MapBrowserEvent#get* methods into properties