Handle `record` keys outside `domain`

[tgfisher4]

Addresses #704.

New behavior is that:

• record.is allows keys outside domain
• record.{en,de}code allow but strip keys outside domain

Other changes:

• added/modified appropriate record tests
  • distinguished HyphenatedString from HyphenatedStringFromNonHyphenated so that the former can be used for (only) testing a domain that is a subset of string, and the latter for testing a prismatic domain
• implement enumerableRecord in terms of exact

Happy to iterate based on feedback.

[gcanti]

@tgfisher4 LGTM

[gcanti]

Thanks @tgfisher4