Add `lto` option to profiles.

Closes #759.
Fix Windows nightly links.

The homepage was linking to outdated nightlies. This had been fixed in the readme, but not on the actual website.
auto merge of #891 : ruud-v-a/cargo/patch-1, r=alexcrichton

The homepage was linking to outdated nightlies. This had been fixed in the readme, but not on the actual website.
Fix panic with plugins and build commands

This fixes a bug in cargo where target executables and libraries would be linked
to plugin native dependencies (not wanted!).

Closes #885
Tighten up the example for a build script
Merge branch 'lto' of https://github.com/BurntSushi/cargo into BurntSushi-lto
hide curl progress output
Polish off the LTO branch
auto merge of #896 : jgillich/cargo/patch-3, r=alexcrichton

Currently the command output looks like this on Fedora:

```
$ curl https://static.rust-lang.org/rustup.sh | sudo bash
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  9866  100  9866    0     0  39592      0 --:--:-- --:--:-- --:--:-- 39622[sudo] password for jakob: 
```
The first time I ran it, I didn't even realize it is asking for a password. By using the options for `silent` and `show-error`, we get this:

```
$ curl -sS https://static.rust-lang.org/rustup.sh | sudo bash
[sudo] password for jakob:
```
And errors are still displayed:

```
$ curl -sS https://example.invalid | sudo bash
curl: (6) Could not resolve host: example.invalid
[sudo] password for jakob: 
```
Directly use python’s urllib instead of curl in etc/dl-snapshot.py
auto merge of #899 : linkmauve/cargo/master, r=alexcrichton
One does not simply `make` Cargo

README fix with correct build instructions for building from source.
auto merge of #900 : steveklabnik/cargo/one_does_not_simply_make_cargo, r=alexcrichton

README fix with correct build instructions for building from source.
auto merge of #894 : alexcrichton/cargo/issue-888, r=brson
auto merge of #893 : alexcrichton/cargo/issue-885, r=brson

This fixes a bug in cargo where target executables and libraries would be linked
to plugin native dependencies (not wanted!).

Closes #885
auto merge of #895 : alexcrichton/cargo/BurntSushi-lto, r=brson

Closes #759, continuation of #790.