Export XYZ source
minZoom is not a supported property of ol.tilegrid.XYZOptions
Adding XYZOptions to objectliterals.jsdoc

I remain uncertain about when to use the @exportClass annotation and when to use the @exportSymbol.  osmsource.exports seems to get away with simply @exportSymbol, but many other sources use @exportProperty.
Moving maxZoom default to XYZ source.

No reason this convenience should be restricted to the OSM layer.
Remove unused require

This was unused before 03f7bb66374b162aab26289b761e7918b79c0ca7 as well.  It would be interesting to see how many other unused requires there are (types that are only referenced in comments but not used in code).
Add example using XYZ tiles from Esri
Merge pull request #979 from tschaub/xyz

Export ol.source.XYZ.