Bump version to 0.11-pre

This also changes some of the download links in the documentation
to 'nightly'.
auto merge of #13296 : brson/rust/0.11-pre, r=alexcrichton

This also changes some of the download links in the documentation
to 'nightly'.
std: TrieSet should implement container::{,Mutable}Set
extra: Add with_capacity to PriorityQueue and SmallIntMap