Add `lto` option to profiles.

Closes #759.
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
Polish off the LTO branch
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.
Update the FAQ and some documentation styles

Closes rust-lang/crates.io#21
Closes rust-lang/crates.io#29
Closes #882