rustdoc: Fix some more broken links
rustdoc: Filter private methods from inlined impls

Closes #14583
mk: Less noisy rustdoc invocations
rustdoc: Ensure external impls are inlined once

If the type associated with the impl is `pub use`'d or referenced twice in a
downstream crate, the impl will attempt to be inlined twice.

Closes #14584
rustdoc: Deduplicate lists of implementors

Inlining caused implementors to show up multiple times.

cc #14584
rustdoc: Correctly inline required/provided methods

Apparently relying on provided_source in ty::Method is unreliable!

Closes #14594
std: add `IterReader` to adapt iterators into readers
std: Remove generics from Option::expect

This commit removes the <M: Any + Send> type parameter from Option::expect in
favor of just taking a hard-coded `&str` argument. This allows this function to
move into libcore.

Previous code using strings with `expect` will continue to work, but code using
this implicitly to transmit task failure will need to unwrap manually with a
`match` statement.

[breaking-change]
Closes #14008
rustdoc: Put primitives in respective modules

The logical location for the documentation of a primitive is in the module that
declared it was a module for that primitive.
syntax: shuffle some allocation out of binop_to_str
Add comments for the token table
libc: only provide an rlib.

There's absolutely no reason for `libc` to be offered as a dynamic
library.
Add code example to std::os::getenv for unix.
Implement Show for RingBuf
Mark the exit of infinite loops as unreachable
Fix an ICE when a function argument is of the bottom type

Fixes #13352
collections: optimize `HashMap`. Add `DefaultResizePolicy`.

Refactored the load factor and the minimum capacity out of HashMap.
The size of HashMap<K, V> is now 64 bytes by default on a 64-bit platform
(or 48 bytes, that is 2 words less, with FNV)
Added a documentation in a few places to clarify the behavior.
std: Improve non-task-based usage

A few notable improvements were implemented to cut down on the number of aborts
triggered by the standard library when a local task is not found.

* Primarily, the unwinding functionality was restructured to support an unsafe
  top-level function, `try`. This function invokes a closure, capturing any
  failure which occurs inside of it. The purpose of this function is to be as
  lightweight of a "try block" as possible for rust, intended for use when the
  runtime is difficult to set up.

  This function is *not* meant to be used by normal rust code, nor should it be
  consider for use with normal rust code.

* When invoking spawn(), a `fail!()` is triggered rather than an abort.

* When invoking LocalIo::borrow(), which is transitively called by all I/O
  constructors, None is returned rather than aborting to indicate that there is
  no local I/O implementation.

* Invoking get() on a TLD key will return None if no task is available

* Invoking replace() on a TLD key will fail if no task is available.

A test case was also added showing the variety of things that you can do without
a runtime or task set up now. In general, this is just a refactoring to abort
less quickly in the standard library when a local task is not found.
syntax: methodify the lexer
syntax: use doc comments in the interner