Clarify that snapshots are automatically retrieved.
Fix usage for rustpkg init

When I took out the ability to make a new project by name, I forgot to
update the usage to reflect the changes.
Update rustpkg manpage to add init.

I didn't update the manpage when I added the init command. Whoops.
auto merge of #9337 : steveklabnik/rust/rustpkg_usage, r=catamorphism

When I took out the ability to make a new project by name, I forgot to
update the usage to reflect the changes.
auto merge of #9327 : larsbergstrom/rust/tutorial_installation_tweak, r=catamorphism

I've had multiple people whom I pointed at the Rust tutorial ask me where to download the snapshot compiler, so I made the text more explicit.
auto merge of #9338 : steveklabnik/rust/rustpkg_update_manpage, r=catamorphism

I didn't update the manpage when I added the init command. Whoops.
auto merge of #9278 : alexcrichton/rust/ndebug, r=brson

Many people will be very confused that their debug! statements aren't working
when they first use rust only to learn that they should have been building with
`--cfg debug` the entire time. This inverts the meaning of the flag to instead
of enabling debug statements, now it disables debug statements.

This way the default behavior is a bit more reasonable, and requires less
end-user configuration. Furthermore, this turns on debug by default when
building the rustc compiler.
auto merge of #9276 : alexcrichton/rust/dox, r=brson

Hopefull this will make our libstd docs appear a little more "full".
Implement a web backend for rustdoc_ng

This large commit implements and `html` output option for rustdoc_ng. The
executable has been altered to be invoked as "rustdoc_ng html <crate>" and
it will dump everything into the local "doc" directory. JSON can still be
generated by changing 'html' to 'json'.

This also fixes a number of bugs in rustdoc_ng relating to comment stripping,
along with some other various issues that I found along the way.

The `make doc` command has been altered to generate the new documentation into
the `doc/ng/$(CRATE)` directories.