rustdoc: Fix inclusion of the new fonts

These fonts were moved into place by rust's makefiles, but rustdoc is widely
used outside of rustc itself. This moves the fonts into the rustdoc binary,
similarly to the other static assets, and writes them to the output location
whenever rustdoc generates documentation.

Closes #13593
Closes #13787
rustdoc: Don't have rustc emit warnings

They're much more useful when building code, much less so when building
documentation.

Closes #13894
rustdoc: Stop requiring a crate ID attribute

This is mostly just an artificial requirement as it can use similar logic to the
compiler to infer the crate id.
rustdoc: Put bangs on the names of macros

This makes them a little easier to search for and makes it clearer that they're
a macro and not an item to import.

Closes #13852
syntax: Fix duplicate attributes on module files

The outer attributes were manually appended when a module file was parsed, but
the attributes were also added higher up the stack of parsing (when the module
finished parsing). This removes the append in parsing the module file.

Closes #13826
rustdoc: Make static initalizers prettier

Previously, if an initializer took multiple lines or was just large in general,
it was pretty poorly rendered [1] [2]. This alters the logic to just link back
to the source for any multi-line static, with a placeholder of "[definition]".
This should make reading statics a little easier on the eyes. All single-line
statics are still inlined in the documentation.

Closes #13198

[1] - http://static.rust-lang.org/doc/master/sync/mutex/index.html#statics
[2] - http://static.rust-lang.org/doc/master/std/sync/atomics/index.html#statics
rustdoc: Allow forcing inlining of `pub use`

Rustdoc currently doesn't inline documentation of a `pub use` if the target is
publicly reachable. This changes rustdoc to allow a #[doc(inline)] attribute to
force inlining the documentation, regardless of whether the targe is public or
not.

Closes #13045
rustdoc: Have no_run imply no_trans

This allows writing code examples which pass all analysis of the compiler, but
don't actually link. A good example is examples that use extern {} blocks.

Closes #12903
rustdoc: Migrate from sundown to hoedown

This primary fix brought on by this upgrade is the proper matching of the ```
and ~~~ doc blocks. This also moves hoedown to a git submodule rather than a
bundled repository.

Additionally, hoedown is stricter about code blocks, so this ended up fixing a
lot of invalid code blocks (ending with " ```" instead of "```", or ending with
"~~~~" instead of "~~~").

Closes #12776
rustdoc: Enable the footnote markdown extension

This enables hoedown's footnote extension, and fixes all footnotes in the
reference manual to use the new syntax.
doc: Remove latex math documentation

This hasn't worked since pandoc stopped being used. We can get by well enough
with the superscript extension for these equations.

Closes #12989
rustdoc: Turn the noise down on implemented traits

This commit removes the inherited documentation from type pages. This generally
just clutters up the page when you can click through to the trait itself to get
all the meaty documentation.

Closes #11991
auto merge of #13914 : alexcrichton/rust/pile-o-rustdoc-fixes, r=brson

Lots of assorted things here and there, all the details are in the commits.

Closes #11712