Clarify spec for scheme

[pombredanne]

We MUST clarify the spec for the scheme component.
This is tracked in these PRs and issues:

• Clarify encoding of colon between scheme and type #361
• Percent encoding spec and : and / #39 (comment)

[johnmhoran]

The scheme component is also tracked (commented on) in

• Add RFC 2119/8174 note and convert terms to uppercase as needed #373 (comment)
• Add RFC 2119/8174 note and convert terms to uppercase as needed #373 (comment)
• Add RFC 2119/8174 note and convert terms to uppercase as needed #373 (comment)

I'm currently working on an update to my last push to the scheme-focused PR, #361, to address these comments.

[johnmhoran]

I pushed my latest update last night to PR #361 -- ready for review.