add jstypes/ pseudo ns - for protocol implementations

[shaunlebron]

A protocol now lists all the types that implement it. Take for example, if a user sees that "numbers" implements a protocol, then wonders what are all the protocols that "numbers" implements, there's no way to see them all in one place—because "numbers" doesn't have a designated API page for listing such a thing.

For that, we should create a jstypes pseudo namespace to list them. See extend-type for primitives:

• nil
• object
• string
• number
• array
• function
• boolean

Constructors:

• js/Date

[shaunlebron]

I think I'd rather just show the implementations for native types in the extra-sources section of the protocol page. There's so few of them right now anyway.