Mark ol.format.GPX#readProjection as a function
Add the jsdoc ol.extent namespace
Merge pull request #2134 from fredj/jsdoc-extent

Add the jsdoc ol.extent namespace
Export ol.format.GML#writeFeatures
Merge pull request #2135 from bartvde/gml-write-export

Export ol.format.GML#writeFeatures
Merge pull request #2119 from fredj/apidoc

Mark ol.format.GPX#readProjection as a function
Clarify that ol.Coordinate is for xy coordinates

Docs only; no logic change
Merge pull request #2137 from probins/patch-1

Clarify that ol.Coordinate is for xy coordinates