Various READMEs and docs cleanup

Noticeably closes #11428.
Trim src/ README, bring back version_info everywhere
Tighten up float literal lexing.

Specifically, dissallow setting the number base for every type of float
literal, not only those that contain the decimal point. This is in line with
the description in the manual.
Add /doc/rustuv to .gitignore
Removed remnants of `@mut` and `~mut` from comments and the type system.
doc: build the docs for librustpkg
Restore missing line breaks in doc/index.html

a30d61b05a removed all of the trailing whitespace in doc/index.md.
Unfortunately, that trailing whitespace was actually markdown syntax for
line breaks.
Add librustuv to doc/index.md
Add inline attributes documentation.

Closes #7959.
more backticks
Don't overwrite the options.output value from build_session_options
Mark allowed dead code and lang items as live

Dead code pass now explicitly checks for `#[allow(dead_code)]` and
`#[lang=".."]` attributes on items and marks them as live if they have
those attributes. The former is done so that if we want to suppress
warnings for a group of dead functions, we only have to annotate the
"root" of the call chain.
Remove RealExt

These functions are of little utility outside a small subset of use cases. If people need them for their own projects then they can use their own bindings for libm (which aren't hard to make).
Clean up std::num::cmath and remove stale comments
Bump version to 0.10-pre
xfail two tests that hang on Android (#11419)
Add Clone to TreeSet
rustc: make error messages containing generic more self-explanatory.

Unsuffixed literals like 1 and 1.1, and free type parameters sometimes
have to be printed in error messages, which ended up with <V0>, <VI0>
and <VF0>. This change puts the words "generic" and "integer"/"float"
into the message so it's not a completely black box.
Better error message for semicolon on the last line of a function

closes #8005
libsyntax: Make managed box `@` patterns obsolete