Missing features megathread

[bplommer]

Ideas from TL submission:

• expose more functionality from the Java SDK
• add support for server-side ScalaJS, backed by the Javascript server SDK
• add support for client-side ScalaJS
• introduce the concept of a codec for reading feature flags to arbitrary types
• introduce a thicker representation of "feature flag", encapsulating feature key, default value and codec
• add a Scala-idiomatic API for constructing evaluation contexts

[Andrea]

Missing a very nice cat related icon! 🐱

[morgen-peschke]

introduce a thicker representation of "feature flag", encapsulating feature key, default value and codec

I've opened #171 for this, though I wasn't able to include the codec without breaking bincompat. There's a circe module in there as well, which may take the pressure off including a codec for those willing to use circe.