SetPositioning exposition in the API

The method in ol.Overlay is not exposed whereas is equivalent
getter getPositioning is visible in API and documentation.
The PR add a line of description to the documentation and expose
the method
Add script to combine examples
Add target to concatenate and build all examples
Only build combined examples in integration tests
Add ol.Map#getEventPixel
Add ol.Map#getEventCoordinate
Export ol.Map#getEventPixel
Export ol.Map#getEventCoordinate
Use getEventPixel in ol.MapBrowserEvent
Use getCoordinatePixel in ol.MapBrowserEvent
Typo describes -> describe
Typo retieving -> retrieving
Merge pull request #1131 from jomue/fix-apidoc-typo

Fix 2 typos on the API docs mainpage
Only call lineTo if we are in a new pixel for linestring

Rendering performance degrades as the context lineWidth increases when calling lineTo many times for the same pixel coordinate.  This appears to be a widespread performance issue and is very clearly improved by only calling lineTo when in a new pixel coordinate.
Avoid calling lineTo on the same pixel for polygon stroke
Export ol.Map#getViewport
Merge pull request #1118 from twpayne/build-examples-together

Build examples together
Merge pull request #1129 from elemoine/eventcoord

Add ol.Map#getEventPixel and ol.Map#getEventCoordinate
Merge pull request #1132 from tschaub/wide-stroke

Only call lineTo if we are in a new pixel.
Align pixels when drawing icons or shapes

The floor before setting the transform ensures that we translate by integer pixels for odd and even dimenstions.  The round before drawing the image ensures pixels are aligned.