Mark ol.format.GPX#readProjection as a function
Fix GoogleMaps example view max zoom levels
Expose the map renderer type to the public API

In the case  where the map decides itself which renderer to use. It can
be convenient for the developer to have knowledge of the choice made.
Rename ol.RendererHint to ol.RendererType
Provide ol.RendererType structure through ol.renderer.Map

It was previously in ol.Map, but it could not be provided because
of circular dependencies.
Rename Map.DEFAULT_RENDER_HINTS to Map.DEFAULT_RENDERER_TYPES
Export ol.ObjectEvent#key property
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.