num: rm wrapping of `Float` methods as functions

The `Float` trait methods will be usable as functions via UFCS, and
we came to a consensus to remove duplicate functions like this a long
time ago.

It does still make sense to keep the duplicate functions when the trait
methods are static, unless the decision to leave out the in-scope trait
name resolution for static methods changes.
syntax: allow stmt/expr macro invocations to be delimited by [].

this is useful for macros like vec! which construct containers
Make libtime fields public
remove the cmath module

This is an implementation detail of the `f32` and `f64` modules and it
should not be public. It renames many functions and leaves out any
provided by LLVM intrinsics, so it is not a sensible binding to the C
standard library's math library and will never be a stable target.

This also removes the abuse of link_name so that this can be switched to
using automatically generated definitions in the future. This also
removes the `scalbn` binding as it is equivalent to `ldexp` when
`FLT_RADIX` is 2, which must always be true for Rust.
auto merge of #13225 : thestinger/rust/num, r=cmr

The `Float` trait methods will be usable as functions via UFCS, and
we came to a consensus to remove duplicate functions like this a long
time ago.

It does still make sense to keep the duplicate functions when the trait
methods are static, unless the decision to leave out the in-scope trait
name resolution for static methods changes.
auto merge of #13234 : seanmonstar/rust/pr/12947, r=alexcrichton

this is useful for macros like vec! which construct containers

rebase of #12947 because I'm impatient.
auto merge of #13240 : sfackler/rust/time-pub, r=alexcrichton
Merge branch 'master' of https://github.com/mozilla/rust