Some documentation fixes and improvements
install: Make the LD_LIRARY_PATH warning more aesthetic
install: Run ldconfig when installing on Unix. Closes #15596.

If ldconfig fails it emits a warning. This is very possible when installing
to a non-system directory, so the warning tries to indicate that it may
not be a problem.
rustdoc: Add stability dashboard

This commit adds a crate-level dashboard summarizing the stability
levels of all items for all submodules of the crate.

The information is also written as a json file, intended for consumption
by pages like http://huonw.github.io/isrustfastyet/

Closes #13541
Bug fixes for stability tracking

This commit adds correct stability tracking for struct fields and
corrects some places where rustdoc was not pulling the stability data.
auto merge of #15586 : aturon/rust/stability-dashboard, r=alexcrichton

This PR adds a crate-level dashboard summarizing the stability levels of all items for all submodules of the crate.

The information is also written as a json file, intended for consumption by pages like http://huonw.github.io/isrustfastyet/

Along the way, fixes a few bugs in stability tracking and places where rustdoc was not pulling the existing stability data.

Closes #13541
auto merge of #15589 : Denommus/rust/master, r=alexcrichton

I have noticed some errors and some absences that I considered essential to the usability of rustc in zsh, so I included them and updated some of the man page.
Only run ldconfig on Linux
auto merge of #15597 : brson/rust/ldconfig, r=pcwalton

If ldconfig fails it emits a warning. This is very possible when installing
to a non-system directory, so the warning tries to indicate that it may
not be a problem.
std: Move MemoryMap fields to methods

If modified, you can safely unmap arbitrary memory. These fields are not
intended to be modified, so read-only accessors are the only ones that are
provided.

Closes #15478
auto merge of #15588 : alexcrichton/rust/issue-15478, r=cmr

If modified, you can safely unmap arbitrary memory. These fields are not
intended to be modified, so read-only accessors are the only ones that are
provided.

Closes #15478
Convert a first batch of diagnostics to have error codes