fluent: Implement Syntax 0.6 in js runtime

[Pike]

Keeping track of changes in fluent 0.6 that could/should be implemented in fluent runtime

• ExternalArgument -> VariableReference
• [DROPPED] Add TermReference
• [DROPPED] (Maybe?) Add VariantList
  • The current parser/resolver should parse VariantLists as Patterns with a selector-less SelectExpression. It may be OK to keep it this way for now.

[stasm]

Hey @zbraniecki, this is the issue about implementing Syntax 0.6 in the runtime parser and resolver. We talked about it yesterday. Let me know if you'd like to take some of the items listed in the description (I added a few more). If not, that's cool, I'll have time early next week to work on this. Thanks!

[stasm]

This landed in master last week and was published as fluent 0.7.0.