Represent enums with regular structs; no more alignment-breaking casts.
Make &self permit explicit lifetimes, but don't really use them
(this will be needed for snapshotting at some point).
Allow constant expressions in [Type * n].
Now actually allow using constants in those constant expressions for [T * n].
Allow expressions that are not just a single value for repeated fixed length vector syntax.
Fix pretty printer for fixed length vectors.
Add tests for const exprs in fixed vec length type and vec repeat.
Make driver::driver::parse_cfgspecs parse any variety of meta_item

All current meta items types (word, name-value, list) are now
properly parsed by rustc --cfg command line. Fixes #2399

Signed-off-by: Luca Bruno <lucab@debian.org>
auto merge of #5112 : luqmana/rust/3469, r=graydon

So this is a partial fix for #3469. Partial because it only works for simple constant expressions like `32/2` and `2+2` and not for any actual constants.

For example:
```
const FOO: uint = 2+2;
let v: [int * FOO];
```

results in:
```
error: expected constant expr for vector length: Non-constant path in constant expr
```

This seems to be because at the point of error (`typeck::astconv`) the def_map doesn't contain the constant and thus it can't lookup the actual expression (`2+2` in this case).

So, feedback on what I have so far and suggestions for how to address the constant issue?
auto merge of #5433 : lucab/rust/lucab/cfgspec, r=graydon

All current meta items types (word, name-value, list) are now
properly parsed by rustc --cfg command line. Fixes #2399
auto merge of #5356 : jld/rust/enum-less-magic, r=graydon

Fixes #1645.
auto merge of #5426 : nikomatsakis/rust/issue-4846-lifetimes-in-expl-self, r=pcwalton

(this will be needed for snapshotting at some point)

r? @pcwalton
rewrite the tutorial section on boxes
auto merge of #5428 : thestinger/rust/tutorial, r=catamorphism

My goal is to explain the underlying concepts first (destructors and then ownership) with plenty of step-by-step examples, so that thoroughly explaining the semantics of mutability, boxes, moves, etc. is a breeze. I'm trying to avoid the comparisons with C++ that were done before, because this should be approachable for people coming from any language. C++ programmers already know these concepts so they aren't the audience that needs to be catered to. Comparisons with other languages can be done in separate documents (like [this one](https://github.com/mozilla/rust/wiki/Rust-for-CXX-programmers)).

This still needs examples for ownership (inherited mutability), owned boxes and managed boxes.
syntax: move ext/deriving.rs to ext/deriving/mod.rs
syntax: split deriving module into submodules for each trait