Change method lookup to require invariance for mutable references

Fixes #17033.
Fixes #15965.
Change ItemModifier and ItemDecorator to traits

For convenience, the traits are implemented for the respective bare
functions. Change code from this:

```rust
ItemDecorator(some_function)
// or
ItemModifier(some_other_function)
```
to
```rust
ItemDecorator(box some_function)
// or
ItemModifier(box some_other_function)
```

[breaking-change]
dave hates jokes :wink:
hello_world.rs -> main.rs
Remove much of the modules section.

This part can get _really_ confusing, and we want to make sure that
people succeed in the guide. I plan on making a module guide in the
future to replace the information here.
remove rich hickey love
don't say 'semantic'
Disable ASLR on Windows, for now.
Escape backslashes in debugger scripts.
Use DWARF4 on Windows.
Fix #17156
Register snapshots
Remove BasicMacroExpander and BasicIdentMacroExpander

The spans inside of these types were always None and never used. Pass
the expander function directly instead of wrapping it in one of these
types.

[breaking-change]
librustc: Make sure region bounds on closures outlive calls to them.

This can break code like:

    fn call_rec(f: |uint| -> uint) -> uint {
        (|x| f(x))(call_rec(f))
    }

Change this code to use a temporary instead of violating the borrow
rules:

    fn call_rec(f: |uint| -> uint) -> uint {
        let tmp = call_rec(|x| f(x)); f(tmp)
    }

Closes #17144.

[breaking-change]
Replace the Tutorial with the Guide.

The Guide isn't 100% perfect, but it's basically complete. It's
certainly better than the tutorial is. Time to start pointing more
people its way.

I also just made it consistent to call all things 'guides' rather than
tutorials.

Fixes #9874. This is the big one.

And two bugs that just go away.

Fixes #14503.
Fixes #15009.
only deprecate the guide rather than :fire: :fire: :fire:
Handle always-unsized structs

closes #16977
Fix bug in padding unicode, #17105.
auto merge of #16657 : steveklabnik/rust/goodbye_tutorial, r=brson

The Guide isn't 100% perfect, but it's basically complete. It's
certainly better than the tutorial is. Time to start pointing more
people its way.

I also just made it consistent to call all things 'guides' rather than
tutorials.

Fixes #9874. This is the big one.

And two bugs that just go away.

Fixes #14503.
Fixes #15009.
librustc: Enum nullable pointer opt should not apply to raw pointers.