Closes #20711

There is likely to be new users with the alpha release, and there are a lot of documents on the internet (StackOverflow, reddit, blogs) that refer to these guides, so emitting a more helpful error than "404" is nice. Hence, I've temporarily reinstated stub documents for each of the old guides, referring to as relevant a part of the book as possible.

Also, rustbook was silently ignoring some errors, which lead to an inconsistency with directory creation/file writing. This meant the CSS file was not being written if no `doc` directory existed in the users build dir (e.g. the buildbots). This should mean that the CSS will appear automatically in later builds.

Here's my PR for the changes discussed in #19823. I decided to leave `_these_` types of italics the way there were because it differentiates the use of italics for emphasis from `*key term*` italics. Otherwise, bolded terms have been changed to italics, and single and double quotes have been changed appropriately, depending on their context (my judgement may not be the best, though).

r? @steveklabnik (congratulations on #19897 being finalized and merged, by the way!)

This will temporarily prevent warnings generated from expanding to code that the
test harness itself uses. This solution will require tweaking around the beta
cycle, but it will prevent spurious warnings for now.

Closes #20823

r? @alexcrichton. This passes tests for me.

This will temporarily prevent warnings generated from expanding to code that the
test harness itself uses. This solution will require tweaking around the beta
cycle, but it will prevent spurious warnings for now.

Closes #20823

The libstd definitions move to libcore, which causes some minor updates there.

Add test for issue #20414

Reviewed-by: alexcrichton

Link to http://rustbyexample.com/

Reviewed-by: steveklabnik

Make rustdoc use the `[_; N]` syntax instead of `[_, ..N]`

Reviewed-by: sfackler

Better iOS support

Reviewed-by: alexcrichton

Changed alignment according to official Apple docs

Now it is possible to run tests on a jailbroken device

- target_word_size -> target_pointer_width
- added armv7 and armv7s targets
- enabled building binaries so tests could be run on a jailbroken device

The URL previously caused the book to require an internet connection to
get the full styling, this should mean no internet is required.

Fixes #19907

Without this, rustbook was failing because it was expecting the
directory to exist. (Previously, rustbook was just silently failing to
install the CSS files due to this.)

Silently ignoring errors is :( so lets not silently ignore them. huon is
:) now.

There are hundreds of stackoverflow answers, reddit posts and blog
articles that link to these documents, so it's a nicer user experience
if they're not plain 404s.

The intention is to let these hang around only for relatively short
while. The alpha is likely to bring in many new users and they will be
reading the documents mentioned above.

Closes #20711

Because we are warning about unstable APIs and there are many
of these yet, this creates a high likelyhood doc tests will
fail.

This doesn't seem right as a blanket policy to me anyway, though
certainly we want it in std. Probably more appropriate to add
a rustdoc option.

Fixes #19907

Because we are warning about unstable APIs and there are many
of these yet, this creates a high likelyhood doc tests will
fail.

This doesn't seem right as a blanket policy to me anyway, though
certainly we want it in std. Probably more appropriate to add
a rustdoc option.

mk: Update prerelase versioning to conform to semver

Reviewed-by: alexcrichton

Fix assertion in Mutex::destroy() on DragonFly (#20698)

Reviewed-by: alexcrichton

bench: fix a few compiler warnings

Reviewed-by: alexcrichton

This commit is an attempt to standardize the use of punctuation and
formatting in "The Rust Programming Language" as discussed in #19823.

- Convert bold text to italicized textcwhen referring to terminology.
- Convert single-quoted text to italicized or double-quoted text,
  depending on context.
- Use double quotes only in the case of scare quotes or quotations.