Validate and escape URI Parameters

[kylef]

See https://github.com/apiaryio/fury-adapter-parser-oas3/pull/40#discussion_r237515513

[honzajavorek]

Addressing this needs some design and coordination across API Elements and the tooling. Related Dredd issues:

• Dredd and Apiary URI Template syntax are not compatible: Dredd and Apiary URI Template syntax are not compatible dredd#1012 (interesting discussions in this one!)
• URL Decode Parameter Names: URL Decode Parameter Names dredd#481
• Conversion of hyphens to %2d in API documentation: Conversion of hyphens to %2d in API documentation dredd#856