Add some doc examples to lib{green,native}

"How do I start in libX" is a common question that I've seen, so I figured
putting the examples in as many places as possible is probably a good idea.
Make semver::Version fields public
Implement std::fmt::Show for semver::{Identifier, Version}
Add new function str::from_utf8_lossy()

from_utf8_lossy() takes a byte vector and produces a ~str, converting
any invalid UTF-8 sequence into the U+FFFD REPLACEMENT CHARACTER.

The replacement follows the guidelines in §5.22 Best Practice for U+FFFD
Substitution from the Unicode Standard (Version 6.2)[1], which also
matches the WHATWG rules for utf-8 decoding[2].

[1]: http://www.unicode.org/versions/Unicode6.2.0/ch05.pdf
[2]: http://encoding.spec.whatwg.org/#utf-8
Hoist path::Display on top of from_utf8_lossy()
auto merge of #12062 : kballard/rust/from_utf8_lossy, r=huonw

`from_utf8_lossy()` takes a byte vector and produces a `~str`, converting
any invalid UTF-8 sequence into the U+FFFD REPLACEMENT CHARACTER.

The replacement follows the guidelines in §5.22 Best Practice for U+FFFD
Substitution from the Unicode Standard (Version 6.2)[1], which also
matches the WHATWG rules for utf-8 decoding[2].

[1]: http://www.unicode.org/versions/Unicode6.2.0/ch05.pdf
[2]: http://encoding.spec.whatwg.org/#utf-8

Closes #9516.
auto merge of #12083 : bjz/rust/semver, r=huonw
Span debugger
Correct span for ExprFnBlock, ExprMethodCall, ExprParen
Add comments to span debugger
auto merge of #12087 : sanxiyn/rust/show-span, r=huonw
Add unimplemented! macro
Add missing test for unreachable! macro
Removed prelude::* from libstd files.

This replaces the imports from the prelude with the re-exported symbols.
Cleaned up imports per coding standards.

No functional changes; just style.
auto merge of #12075 : chromatic/rust/gh_11983_deglob_std, r=alexcrichton

This replaces the imports from the prelude with the re-exported symbols.
Clean up formatting in macros module
Added tests to make tidy
auto merge of #12055 : dguenther/rust/tidy_test, r=alexcrichton

This PR extends the tidy formatting check to rust files in the test folder. To facilitate this, a few flags were added to tidy:

* `xfail-tidy-cr` - Disables the check for CR characters for all following lines in the file
* `xfail-tidy-tab` - Disables the check for tab characters for all following lines in the file
* `xfail-tidy-linelength` - Disables the line length check for all following lines in the file

Checks should not have to be disabled often. I disabled line length checks in `debug-info` tests that use `debugger:` checks, but aside from that, there were relatively few exclusions. Running tidy on all the tests does slow down the formatting check, so it may be worth investigating further optimization.

cc #4534
doc: add license information for gen. files