More 0.7 release notes
Show defaults in rustdoc usage message
fix text of tutorials
Update AUTHORS.txt
Minor doc updates to reflect #[deriving(Zero)], and small release notes adjustments.

The `extra::fileinput` module landed just after 0.6 was released, and there are many
more derivable traits.
Usable instructions for generating docs from source
rustc: Fix formatting of --help
Merge pull request #7270 from thestinger/doc

accumulated doc pull requests from the queue