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
Adding show impl for Rc
std: add `IterReader` to adapt iterators into readers
Add next_permutation and prev_permutation onto MutableOrdVector<T>.

Unlike ImmutableClonableVector::permutations() which returns an iterator,
cloning the entire array each iteration, these methods mutate the vector in-place.
For that reason, these methods are much faster; between 35-55 times faster,
depending on the benchmark. They also generate permutations in lexicographical order.
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
auto merge of #14616 : forticulous/rust/rc-show, r=alexcrichton

Show impl for Rc
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.