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
Improvements to externs readme
Merge pull request #2139 from probins/patch-2

Improvements to externs readme.
Clarify compiler exports in tasks readme
Export method to get resolution for extent and size

While this is straightforward to calculate, this method adds convenience.
Merge pull request #2141 from probins/patch-5

Clarify compiler exports in tasks readme.
Merge pull request #2142 from tschaub/res-for-extent

Export method to get resolution for extent and size.