Fixed broken link to agi's Terrain Server product page.
Updated quanitzed-mesh format to include the definition of the ExtensionFlags and Oct-Encoded Vertex Normals.
Added the Accept header required for requesting vertex normals.
Update QuantizedMesh extension format. In place of using a bitfield identifying the presence of an extension, all extensions must start with a unique id followed by a 32 bit length of the extension, followed by the extension bytes. This new format allows for clients to skip over extensions that it does not know of or care to unpack.
Revised oct-encoded vertex normal extension to include the changes introduced in https://github.com/AnalyticalGraphicsInc/cesium/pull/2291
Merge remote-tracking branch 'agi/master' into quantizedMeshOctVertexNormals

Conflicts:
	terrain/formats/quantized-mesh-1.0.html
Merge pull request #5 from abwood/quantizedMeshOctVertexNormals

Quantized mesh oct vertex normals