This commit adds support to rustbuild to run all documentation tests, basically
running `rustdoc --test` over all our documentation. This also includes support
for running the error index tests.
This adds checks to ensure that:
* link anchors refer to existing id's on the target page
* id's are unique within an html document
* page redirects are valid
A few categories:
* Links into compiler docs were just all removed as we're not generating
compiler docs.
* Move up one more level to forcibly go to std docs to fix inlined documentation
across the facade crates.
The current version of hoedown treats lists interrupting paragraphs in the Markdown.pl style rather than CommonMark, so a newline is needed for the list to be rendered properly.
An automated script was run against the `.rs` and `.md` files,
subsituting every occurrence of `task` with `thread`. In the `.rs`
files, only the texts in the comment blocks were affected.
Changes the style guidelines regarding unit tests to recommend using a
sub-module named "tests" instead of "test" for unit tests as "test"
might clash with imports of libtest.
