auto merge of #13296 : brson/rust/0.11-pre, r=alexcrichton
auto merge of #13296 : brson/rust/0.11-pre, r=alexcrichton

This also changes some of the download links in the documentation
to 'nightly'.

shepmaster/rand,bhickey/rand,retep998/rand,GrahamDennis/rand,arthurprs/rand,waynenilsen/rand,bluss/rand,huonw/rand,ebfull/rand,achanda/rand