remove standard library information from the Rust manual

[thestinger]

I think this should be a language specification, and should avoid describing the library. The language semantics and grammar are a much saner scope to cover than the entire standard library. Implementation details like the standard library's choice of allocator are even more out of place.

[brson]

Generally agree with this, though I think the language's interface to the library (intrinsics, lang items, possibly built-in syntax extensions) is in scope, but non-normative (unstable).

[brson]

I don't know what parts of std are described in the manual, having not read it in a long time.

[thestinger]

@brson: I opened this based on it describing the runtime's memory allocation as using malloc and free. It's not actually a guarantee we provide, and I find it way out of scope of the manual.

I think it would be a good idea to cover intrinsics and lang items there too. However, we can probably get rid of the built-in syntax extensions as a language feature now that they can be dynamically loaded. It might need some tweaking to make it an invisible change to users of the standard library.

[steveklabnik]

We now say

This document also does not serve as a reference to the standard library included in the language distribution. Those libraries are documented separately by extracting documentation attributes from their source code.

We do still mention malloc and free, but isn't that now true?

I'd love some clarity here.