Fixed small crossref issues
Orientation check against OrientationLockType (close #235)
consolidated start_url processing (closes #236)
Merge pull request #238 from w3c/well-known-example

Small bug fixes...
Obtaining a manifest should be before processing #234.
Consolidate the following under 'Associating a resource with a manifest':
* Linking to a manifest
* The "manifest.json" well-known URI
(IANA considerations now only has the bits required for registration)
Split the Manifest section into two top-level sections:
* Manifest processing model
* Manifest members
Add a brief intro to the Manifest processing model.
Move Extensibility into Conformance.
Clarify proprietary extensions refer to new members.