tutorial: remove duplicate link references.

`pandoc` issues warnings.

```
pandoc: Duplicate link reference `[macros]' "source" (line 2151, column 1)
pandoc: Duplicate link reference `[tasks]' "source" (line 2150, column 1)
pandoc: Duplicate link reference `[wiki-start]' "source" (line 92, column 1)
```
tutorial: remove unused link references.
Add documentation about mutable statics to rust.md
stop initializing ref_count for stack closures

the only part of the header ~fn and &fn should be touching right now is
the tydesc
rm unused visit_str method from TyVisitor
rm unnecessary stage0 `zero_memory` fn
fix repr of unique vectors with stage0 libstd

Closes #7860
fix repr of @mut vectors
repr: add a test case for @mut inside another type
hashmap: Remove .consume() has rename .consume_iter() to .consume()

Updated all users of HashMap, HashSet old .consume() to use .consume()
with a for loop.

Since .consume() takes the map or set by value, it needs awkward
extra code to in librusti's use of @mut HashMap, where the map value can
not be directly moved out.
auto merge of #7842 : thestinger/rust/closure, r=huonw
auto merge of #7833 : blake2-ppc/rust/hashmap-consume, r=alexcrichton

Updated all users of HashMap, HashSet ::consume() to use
.consume_iter().

Since .consume_iter() takes the map or set by value, it needs awkward
extra code to in librusti's use of @mut HashMap, where the map value can
not be directly moved out.

Addresses issue #7719
auto merge of #7845 : gifnksm/rust/tutorial-remove-dup, r=cmr

`pandoc` issues warnings.

```
pandoc: Duplicate link reference `[macros]' "source" (line 2151, column 1)
pandoc: Duplicate link reference `[tasks]' "source" (line 2150, column 1)
pandoc: Duplicate link reference `[wiki-start]' "source" (line 92, column 1)
```

This PR also removes unused link references.
auto merge of #7846 : alexcrichton/rust/static-mut-dox, r=pnkfelix

It's probably a good idea to at least *mention* them somewhere.
Merge branch 'master' of github.com:mozilla/rust