Fix repeated module documentation
Refactor ty_str to use a ~(str) representation.

Similar to my recent changes to ~[T]/&[T], these changes remove the vstore abstraction and represent str types as ~(str) and &(str). The Option<uint> in ty_str is the length of the string, None if the string is dynamically sized.
std: Add more docs to `std::mem::replace`.
Fixed typo in std::vec
auto merge of #13821 : aochagavia/rust/pr3, r=alexcrichton
auto merge of #13797 : lifthrasiir/rust/std-mem-replace-doc, r=alexcrichton

Inspired by @steveklabnik's [comment](http://www.reddit.com/r/rust/comments/240p9s/eli5_stdmemreplace/ch2gxw8), this PR adds the practical use cases to the documentation of `std::mem::replace`.

Caveat: We need a `compile-fail` equivalent for doctest. :p
rustdoc: Make strip_hidden use a dedicated hidden item if any.

fixes #13806.
auto merge of #13812 : alxgnon/rust/master, r=alexcrichton

This is a quick fix for repeated documentation descriptions in certain modules.
Following is a list of the faulty modules I found. I ran `pcregrep -r -M "<p>(.+)\n\1" doc` on the html documentation to help identify them.

- [rustuv::uvio](http://static.rust-lang.org/doc/master/rustuv/uvio/index.html)
- [rustuv::uvll](http://static.rust-lang.org/doc/master/rustuv/uvll/index.html)
- [std::rt::backtrace](http://static.rust-lang.org/doc/master/std/rt/backtrace/index.html)
- [std::rt::env](http://static.rust-lang.org/doc/master/std/rt/env/index.html)
- [std::rt::global_heap](http://static.rust-lang.org/doc/master/std/rt/global_heap/index.html)
- [std::rt::local_heap](http://static.rust-lang.org/doc/master/std/rt/local_heap/index.html)
- [std::rt::rtio](http://static.rust-lang.org/doc/master/std/rt/rtio/index.html)
- [std::rt::task](http://static.rust-lang.org/doc/master/std/rt/task/index.html)
- [std::rt::thread](http://static.rust-lang.org/doc/master/std/rt/thread/index.html)
- [std::rt::unwind](http://static.rust-lang.org/doc/master/std/rt/unwind/index.html)
- [syntax::parse::classify](http://static.rust-lang.org/doc/master/syntax/parse/classify/index.html)
- [syntax::parse::common](http://static.rust-lang.org/doc/master/syntax/parse/common/index.html)

After a little testing, I discovered that moving the documentation inside (`//!`) instead of outside (`///`) modules fixed the immediate problem. I went through the trouble of moving the documentation, and with this commit there are no more repeated descriptions within those faulty modules.

This does not fix the underlying problem though. We should look into why having the documentation outside instead of inside caused the descriptions to be repeated. I will create a separate issue with my findings on the subject if necessary.
In the meantime, this simple fix should be enough.
auto merge of #13819 : nick29581/rust/ty_str, r=pcwalton

Similar to my recent changes to ~[T]/&[T], these changes remove the vstore abstraction and represent str types as ~(str) and &(str). The Option<uint> in ty_str is the length of the string, None if the string is dynamically sized.
rustdoc: Make going back in browser history work after typing a search term
auto merge of #13827 : lifthrasiir/rust/rustdoc-hidden-pub-field, r=alexcrichton

Fixes #13806. Also adds a note to `HiddenStructField` about why it doesn't appear in the `clean` module itself.
auto merge of #13830 : noamraph/rust/doc-browser-history, r=kballard

Currently, in both chrome and firefox, if I type something in the search box in the reference docs I get immediately the search results. That's great. However, if I want to go back to the doc I was reading and try to press the back button, I am immediately forwarded again to the search results. This is caused by the fact that the search term is (deliberately) left in the search box, and the search() function is called as if I typed the search term again.
I disabled calling the search() function if there's no search term in the URL, and now it seems to work fine.

I hope I'm sending the pull request correctly - I'm not really used to git and github.
Remove internal support for fixed length strings
auto merge of #13834 : nick29581/rust/str_fix, r=luqmana