document the "built-in trait impls" and where they live

[nikomatsakis]

Issues #363 and #368 describe adding support for various bits of "well-known, builtin" stuff, but it's hard to track completion with two independent lists. What we really need is a matrix. Moreover, it'd be useful for that matrix to be in the chalk book, and able to track not only what is done but where the various impls and things live.

This issue is for adding something to the chalk book (it will require a touch of research) that has roughly this form:

Type	Copy	Clone	Sized	Unsize	Unpin	auto-traits
tuple types
scalar types
closures
...
user-defined structs, enums

with the following key:

• ✅ -- in chalk, fully implemented
• ⚪ -- in chalk, but not implemented
• 📚 -- in the stdlib, no built-in impls needed (book == library, get it!)

OK, you can make up your own key I suppose. =) But I do like emojis!