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
libstd: Change `slice_shift_char`, `shift_char`, `pop_char`, `shift_byte` and `pop_byte` to return an Option instead of failing
libstd: Add unit tests for `slice_shift_char`
libstd: Update docs for `slice_shift_char` and {shift,pop}_{char,byte}
fs: use an iterative algorithm for 'mkdir_recursive'

as requested in #6109
fs: use an iterative algorithm for 'rmdir_recursive'

For now, the windows version uses stat, just as before.
We should switch back to lstat as soon as #12795 is closed.
fs: units tests for mkdir_recusive and rmdir_recursive

The rmdir test is blocked by #12795 on windows.
rustc: Support various flavors of linkages

It is often convenient to have forms of weak linkage or other various types of
linkage. Sadly, just using these flavors of linkage are not compatible with
Rust's typesystem and how it considers some pointers to be non-null.

As a compromise, this commit adds support for weak linkage to external symbols,
but it requires that this is only placed on extern statics of type `*T`.
Codegen-wise, we get translations like:

    // rust code
    extern {
        #[linkage = "extern_weak"]
        static foo: *i32;
    }

    // generated IR
    @foo = extern_weak global i32
    @_some_internal_symbol = internal global *i32 @foo

All references to the rust value of `foo` then reference `_some_internal_symbol`
instead of the symbol `_foo` itself. This allows us to guarantee that the
address of `foo` will never be null while the value may sometimes be null.

An example was implemented in `std::rt::thread` to determine if
`__pthread_get_minstack()` is available at runtime, and a test is checked in to
use it for a static value as well. Function pointers a little odd because you
still need to transmute the pointer value to a function pointer, but it's
thankfully better than not having this capability at all.
Added convenience methods and accompanying tests to the Json class.

Fixed some styling issues with trailing whitespace.

- Removed redundant functions.
- Renamed `get` to `find`
- Renamed `get_path` to `find_path`
- Renamed `find` to `search`
- Changed as_object and as_list to return Object and List
  rather than the underlying implementation types
  of TreeMap<~str,Json> and ~[Json]
- Refactored find_path to use a fold() instead of recursion

Formatting fixes.

Fixed spacing, deleted comment.

Added convenience methods and accompanying tests to the Json class.

Updated tests to expect less pointer indirection.
doc: auto-generate LaTeX includes
doc: remove outdated tutorial entry, restore removed Makefile entries
auto merge of #12556 : alexcrichton/rust/weak-linkage, r=brson

It is often convenient to have forms of weak linkage or other various types of
linkage. Sadly, just using these flavors of linkage are not compatible with
Rust's typesystem and how it considers some pointers to be non-null.

As a compromise, this commit adds support for weak linkage to external symbols,
but it requires that this is only placed on extern statics of type `*T`.
Codegen-wise, we get translations like:

```rust
    // rust code
    extern {
        #[linkage = "extern_weak"]
        static foo: *i32;
    }

    // generated IR
    @foo = extern_weak global i32
    @_some_internal_symbol = internal global *i32 @foo
```

All references to the rust value of `foo` then reference `_some_internal_symbol`
instead of the symbol `_foo` itself. This allows us to guarantee that the
address of `foo` will never be null while the value may sometimes be null.

An example was implemented in `std::rt::thread` to determine if
`__pthread_get_minstack()` is available at runtime, and a test is checked in to
use it for a static value as well. Function pointers a little odd because you
still need to transmute the pointer value to a function pointer, but it's
thankfully better than not having this capability at all.

Thanks to @bnoordhuis for the original patch, most of this work is still his!
auto merge of #12780 : zslayton/rust/json-nav, r=alexcrichton

This is my first non-docs contribution to Rust, so please let me know what I can fix. I probably should've submitted this to the mailing list first for comments, but it didn't take too long to implement so I figured I'd just give it a shot.

These changes are modeled loosely on the [JsonNode API](http://jackson.codehaus.org/1.7.9/javadoc/org/codehaus/jackson/JsonNode.html) provided by the [Jackson JSON processor](http://jackson.codehaus.org/).

Many common use cases for parsing JSON involve pulling one or more fields out of an object, however deeply nested. At present, this requires writing a pyramid of match statements. The added methods in this PR aim to make this a more painless process.

**Edited to reflect final implementation**

Example JSON:
```json
{
    "successful" : true,
    "status" : 200,
    "error" : null,
    "content" : {
        "vehicles" : [
            {"make" : "Toyota", "model" : "Camry", "year" : 1997},
            {"make" : "Honda", "model" : "Accord", "year" : 2003}
        ]
    }
}
```

Accessing "successful":
```rust
 let example_json : Json = from_str("...above json...").unwrap();
 let was_successful: Option<bool> = example_json.find(&~"successful").and_then(|j| j.as_boolean());
```

Accessing "status":
```rust
 let example_json : Json = from_str("...above json...").unwrap();
 let status_code : Option<f64> = example_json.find(&~"status").and_then(|j| j.as_number());
```

Accessing "vehicles":
```rust
 let example_json : Json = from_str("...above json...").unwrap();
 let vehicle_list: Option<List> = example_json.search(&~"vehicles").and_then(|j| j.as_list());
```

Accessing "vehicles" with an explicit path:
```rust
 let example_json : Json = from_str("...above json...").unwrap();
 let vehicle_list: Option<List> = example_json.find_path(&[&~"content", &~"vehicles"]).and_then(|j| j.as_list());
```

Accessing "error", which might be null or a string:
```rust
 let example_json : Json = from_str("...above json...").unwrap();
 let error: Option<Json> = example_json.find(&~"error");
 if error.is_null() { // This would be nicer as a match, I'm just illustrating the boolean test methods
    println!("Error is null, everything's fine.");
 } else if error.is_str(){
    println!("Something went wrong: {}", error.as_string().unwrap());
}
```

Some notes:
* Macros would help to eliminate some of the repetitiveness of the implementation, but I couldn't use them due to #4621. (**Edit**: There is no longer repetitive impl. Methods were simplified to make them more composable.)
* Would it be better to name methods after the Json enum type (e.g. `get_string`) or the associated Rust built-in? (e.g. `get_str`)
* TreeMap requires its keys to be &~str. Because of this, all of the new methods required &~str for their parameters. I'm uncertain what the best approach to fixing this is: neither demanding an owned pointer nor allocating within the methods to appease TreeMap's find() seems desirable. If I were able to take &str, people could put together paths easily with `"foo.bar.baz".split('.').collect();` (**Edit**: Follow on investigation into making TreeMap able to search by Equiv would be worthwhile.)
* At the moment, the `find_<sometype>` methods all find the first match for the provided key and attempt to return that value if it's of the specified type. This makes sense to me, but it's possible that users would interpret a call to `find_boolean("successful")` as looking for the first "successful" item that was a boolean rather than looking for the first "successful" and returning None if it isn't boolean. (**Edit**: No longer relevant.)

I hope this is helpful. Any feedback is appreciated!
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.