readme: Link 'Using' wiki page instead of 'Getting started'.

The Windows-specific instruction under 'Quick Start' linked the wiki article on getting started developing Rust itself, but the quick start is just about obtaining a working Rust installation. The actual wiki page with Windows-specific instructions was difficult to find.
In sieve example, end iteration sooner

The Sieve algorithm only requires checking all elements up to and including the square root of the maximum prime you're looking for. After that, the remaining elements are guaranteed to be prime.
Update README.md

Added 64-bit Windows support to the list of platforms. Support for 64-bit Windows was added in Rust 0.12.0. See  https://mail.mozilla.org/pipermail/rust-dev/2014-October/011267.html for the release notes.
Teach libsyntax about `while let`
Desugar `while let` into `loop { match { ... } }`
Move `while let` behind `while_let` feature gate
Handle `while let` desugaring
Add tests for `while let`
Add `while let` to the reference

Closes #17687
Use explicit case rather than catch-all
fix shootout-mandelbrot to make it pass the shootout test
Remove an unnecessary binary file.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Make the diagnostic for static variables in patterns better

Fixes #17933.
optimize position independent code in executables

Position independent code has fewer requirements in executables, so pass
the appropriate flag to LLVM in order to allow more optimization. At the
moment this means faster thread-local storage.
Continue cfg syntax transition

All deprecation warnings have been converted to errors. This includes
the warning for multiple cfgs on one item. We'll leave that as an error
for some period of time to ensure that all uses are updated before the
behavior changes from "or" to "and".
auto merge of #17948 : jakub-/rust/issue-17933, r=alexcrichton

Fixes #17933.
auto merge of #17957 : TeXitoi/rust/fix-mandelbrot, r=alexcrichton
auto merge of #17975 : thestinger/rust/fPIE, r=eddyb

Position independent code has fewer requirements in executables, so pass
the appropriate flag to LLVM in order to allow more optimization. At the
moment this means faster thread-local storage.
auto merge of #17963 : sfackler/rust/cfg-error, r=alexcrichton

All deprecation warnings have been converted to errors. This includes
the warning for multiple cfgs on one item. We'll leave that as an error
for some period of time to ensure that all uses are updated before the
behavior changes from "or" to "and".
auto merge of #17965 : omasanori/rust/remove, r=sfackler