Add plane type and update functions that accepted plane normal and constant to use the plane type.
Update CHANGES.md.
Merge pull request #504 from AnalyticalGraphicsInc/plane

Plane
Eliminated allocations when setting matrix uniforms
Changes based on review
Merge pull request #506 from AnalyticalGraphicsInc/uniforms

Eliminated allocations when setting matrix uniforms
Update Plane distance parameter doc.
Merge remote-tracking branch 'origin/master' into models