Get the OES_texture_float_linear extension.

There's a bug in most WebGL implementations that the OES_texture_float
extension is not supposed to allow the various LINEAR filtering modes.
To filter a floating point texture with linear filtering requires
enabling OES_texture_float_linear.

This CL does that. The code has not been updated to actually
check the extension exists and doing or disallowing the appropriate
features.

Enabling it will mean on desktop things just work as they did before.

On mobile/tablets it's far more likley OES_texture_float_linear
does not exist
Added STL exporter which can export a whole scene, or the given meshes to STL file format.
Merge remote-tracking branch 'kovacsv/STLExporter' into dev
Merge remote-tracking branch 'greggman/get-texture-float-linear' into dev
Updated builds.
Mover WebGLRenderer2 to examples folder.
Simplified PDBLoader.
Simplified includes for css3d build.
Miscelaneous fixes
Fix SkinnedMesh so that it can be used with BufferGeometry

THREE.SkinnedMesh previously assumed its geometry was an instance of THREE.Geometry while normalizing skinning weights
Added css3d sprites example.
css3d examples improvements.
Merge remote-tracking branch 'WestLangley/dev-misc' into dev
Updated builds.
Merge remote-tracking branch 'rmx/dev' into dev
Clean up and updated builds.
Removed unmaintained includes file.