Stop mspointer events

Stop mspointerup and mspointerdown events reaching the "stop event" overlay container.
Export ol.extent.createEmpty function
Merge pull request #1159 from twpayne/export-create-empty

Export ol.extent.createEmpty function
Add default stability level to docs of exported things.
Fix error in map docs
[ci skip]
Merge pull request #1171 from probins/mapdocs

Fix error in map docs.
Merge pull request #1163 from pagameba/doc-stability

Add default stability level to docs of exported things.
Merge pull request #1147 from elemoine/issue-1147

IE 10 Click on popup
Small addition to view2d docs
Merge pull request #1177 from probins/viewdocs

Small addition to view2d docs.
Fix getImageElement calls in canvas and webgl renderer
Merge pull request #1184 from oterral/get_image_element

Fix getImageElement calls in canvas and webgl renderer