doc: remove node.js dependency

`prep.js` outputs its own HTML directives, which `pandoc` cannot
recognize when converting the document into LaTeX (this is why the
PDF docs have never been highlighted as of now).

Note that if we were to add the `.rust` class to snippets, we could
probably use pandoc's native highlighting capatibilities i.e. Kate.
doc: have a real switch b/w LaTeX compilers
doc: CSS fixes

- fixup and refactor highlighting code
- have a proper print stylesheet
doc: auto-generate LaTeX includes
doc: remove outdated tutorial entry, restore removed Makefile entries
auto merge of #12783 : adrientetar/rust/more-docs, r=alexcrichton

- remove `node.js` dep., it has no effect as of #12747 (1)
- switch between LaTeX compilers, some cleanups
- CSS: fixup the print stylesheet, refactor highlighting code (2)

(1): `prep.js` outputs its own HTML directives, which `pandoc` cannot recognize when converting the document into LaTeX (this is why the PDF docs have never been highlighted as of now).

Note that if we were to add the `.rust` class to snippets, we could probably use pandoc's native highlighting capatibilities i.e. Kate ([here is](http://adrientetar.github.io/rust-tuts/tutorial/tutorial.pdf) an example of that).

(2): the only real highlighting change is for lifetimes which are now brown instead of red, the rest is just refactor of twos shades of red that look the same.
Also I made numbers highlighting for src in rustdoc a tint more clear so that it is less bothering.

@alexcrichton, @huonw

Closes #9873. Closes #12788.
std: Move rand to librand.

This functionality is not super-core and so doesn't need to be included
in std. It's possible that std may need rand (it does a little bit now,
for io::test) in which case the functionality required could be moved to
a secret hidden module and reexposed by librand.

Unfortunately, using #[deprecated] here is hard: there's too much to
mock to make it feasible, since we have to ensure that programs still
typecheck to reach the linting phase.
Remove the dependence of std::io::test on rand.

This replaces it with a manual "task rng" using XorShift and a crappy
seeding mechanism. Theoretically good enough for the purposes
though (unique for tests).
Update users for the std::rand -> librand move.
rand: deprecate `rng`.

This should be called far less than it is because it does expensive OS
interactions and seeding of the internal RNG, `task_rng` amortises this
cost. The main problem is the name is so short and suggestive.

The direct equivalent is `StdRng::new`, which does precisely the same
thing.

The deprecation will make migrating away from the function easier.
auto merge of #12650 : huonw/rust/librand, r=alexcrichton

Move std::rand to a separate rand crate

This functionality is not super-core and so doesn't need to be included
in std. It's possible that std may need rand (it does a little bit now,
for io::test) in which case the functionality required could be moved to
a secret hidden module and reexposed by librand.

Unfortunately, using #[deprecated] here is hard: there's too much to
mock to make it feasible, since we have to ensure that programs still
typecheck to reach the linting phase.

Also, deprecates/removes `rand::rng` (this time using `#[deprecated]`), since it's too easy to accidentally use inside a loop, making things very slow (have to read randomness from the OS and seed the RNG each time.)
Bundle libbacktrace with the compiler

This will soon be used to print backtraces on failure
Add basic backtrace functionality

Whenever a failure happens, if a program is run with
`RUST_LOG=std::rt::backtrace` a backtrace will be printed to the task's stderr
handle. Stack traces are uncondtionally printed on double-failure and
rtabort!().

This ended up having a nontrivial implementation, and here's some highlights of
it:

* We're bundling libbacktrace for everything but OSX and Windows
* We use libgcc_s and its libunwind apis to get a backtrace of instruction
  pointers
* On OSX we use dladdr() to go from an instruction pointer to a symbol
* On unix that isn't OSX, we use libbacktrace to get symbols
* Windows, as usual, has an entirely separate implementation

Lots more fun details and comments can be found in the source itself.

Closes #10128