std: uniform modules titles for doc

This commit uniforms the short title of modules provided by libstd,
in order to make their roles more explicit when glancing at the index.

Signed-off-by: Luca Bruno <lucab@debian.org>
Add docs for more crates
Add a compiler-docs target
Fix rustdoc bug involving PatLit
auto merge of #11177 : cmr/rust/native_and_green_docs, r=alexcrichton

Some people have requested this, and I think it's quite useful to have
documentation for the compiler libraries. libnative and libgreen are
self-explanatory I think.
auto merge of #11134 : lucab/rust/lucab/libstd-doc, r=cmr

Uniform the short title of modules provided by libstd, in order to make their roles more explicit when glancing at the index.
Rename pkgid variables
Rename PkgId to CrateId
Rename uses of PkgId to CrateId in librustpkg
Update Docs to use crateid