Feature: Reference Instructions

[bushidocodes]

This is a higher-level post MVP feature that may not make sense for us. The idea of a reference is that a WebAssembly sandbox can be passed an opaque host reference that it can manage.

• ref.null
• ref.is_null
• ref.func

References:

• https://webassembly.github.io/spec/core/syntax/types.html#syntax-reftype
• https://webassembly.github.io/spec/core/syntax/instructions.html#reference-instructions
• https://github.com/WebAssembly/reference-types/blob/master/proposals/reference-types/Overview.md