This should really fix rust-lang/rust#17528.

Markdown tables require a header, and we don't want one.

Fixes #17528

remove unneeded `pre.rust a' selector

move transform into `.test-arrow`

fixes #16138

So that we have freestanding docs.

A margin for the top level list was leaking into nested ones.

There is no space between the TOC and the succeeding para.

This grows a new option inside of rustdoc to add the ability to submit examples
to an external website. If the `--markdown-playground-url` command line option
or crate doc attribute `html_playground_url` is present, then examples will have
a button on hover to submit the code to the playground specified.

This commit enables submission of example code to play.rust-lang.org. The code
submitted is that which is tested by rustdoc, not necessarily the exact code
shown in the example.

Closes #14654

- Avoids cross-domain requests restrictions
- Better availability of content
- No HTML queries needed for an offline build

Conflicts:
	src/doc/rust.md

- fixup and refactor highlighting code
- have a proper print stylesheet

This converts it to be very similar to crates.mk, with a single list of
the documentation items creating all the necessary bits and pieces.

Changes include:
- rustdoc is used to render HTML & test standalone docs
- documentation building now obeys NO_REBUILD=1
- testing standalone docs now obeys NO_REBUILD=1
- L10N is slightly less broken (in particular, it shares dependencies
  and code with the rest of the code)
- PDFs can be built for all documentation items, not just tutorial and
  manual
- removes the obsolete & unused extract-tests.py script
- adjust the CSS for standalone docs to use the rustdoc syntax
  highlighting

We generate documentation into the doc/ directory, so we shouldn't be
intermingling source files with generated files

CodeMirror parser errors are related to #9873.

Closes #10330.

Cleanup, edit, add some Bootstrap v3.0.0 elements.