First-class types

[jonhue]

Investigate making types first-class citizens. This would involve

• adding a Type primitive type
• removing the type keyword (or using it solely for defining datatypes with constructors)
• perhaps removing all separation between terms, patterns, and types

Ensure

• distinct features are still available, like:
  • default arguments for patterns
  • rest patterns
  • (type annotations within patterns)
  • certain type operators like conditional types, access types, keyof, typeof, optional types