Add an example that renders a simple fractal

This works at resolutions where simplification is significantly reducing the number of points in the line.  At high resolutions, navigation becomes unresponsive.  Limiting draw instructions to a replay group's extent will fix this.
Keep track of max extent for replay
Determining coordinate relationship to extent
Testing segment intersection with extent

If needed, this function can be modified to take two additional coorinates that will be set to the intersection points.
Skip coordinates that don't affect the rendered extent

Segments that intersect the replay group's extent are drawn.  Any segment that represents a change in coordinate-extent relationship is drawn.  This maintains the left/right relationship (or cross product) between points in the rendered extent and every rendered segment.

Still left undone: clip the replay group's rendering to the max extent.
Clip to max extent
Function for applying a 2d transform to an extent
Add geojson sample files
Add vector label example
Update vector-labels example

Add forms to let the user change the labels as they want.
Text 'Wrap' doesn't work properly. '\n' are supposed to allow
line to break.
Remove unused 'align' column from geojson
Update vector-labels example

Add note about the 'Text/Wrap' option currently not working.
Fix vector-labels example

Typo fixes, add 1 more font
Support minPointsPerRing and default to 3
Transform extent coordinates before clipping
Set overlay map in 'add' and 'remove' event handler
Set interaction map in 'add' and 'remove' event handler
Set control map in 'add' and 'remove' event handler
Dispatch 'render' event in renderer.canvas.VectorLayer

The context property of the event only contains the vector rendering.
Add ol.layer.Heatmap class and example