preliminary Linux ARM support
Fixed type signature of uninhabited method.

Added unit test to prevent similar mistakes from happening again. The
previous method was wrong because it dereferenced a pointer to a void type to
match on the result. No self pointer was needed, and the correct method
signature took the self value by value.
core::rt: Remove Close trait

We will just use RAII for now.
core::rt: Fix a warning about unnecessary mutable variable
core::rt: Begin implementing TcpStream

This ended up touching a lot of code related to error handling.
core::rt: Clean up the interface to rtio

Make names that better match rt::io. Return error types.
core::rt: Improve docs
core::rt Restructure some modules

Put all uv code under rt::uv, as if it were in its own crate.
Pull local_sched out of rt::sched.
Move `position` and `rposition` methods to `ImmutableVector` trait
libstd: impl Num for BigUint/BigInt
Update .gitignore
libstd: impl `Orderable` for `BigUint`/`BigInt`
libstd: `Rational` requires `Integer` as type bounds instead of `Num`
libstd: `Ratio` requires `Clone` instead of `Copy`

This allows creating `Ratio<T>` which `T` is non-implicitly copyable types
such as `BigInt`.
libstd: Add tests for BigRational
Replace shared/unique by managed/owned in the tutorial
Issue #5967: Make rvalues mutable
Add explanatory comment to is_rvalue_or_immutable()
Use static string with fail!() and remove fail!(fmt!())

fail!() used to require owned strings but can handle static strings
now. Also, it can pass its arguments to fmt!() on its own, no need for
the caller to call fmt!() itself.
Fix cosmetics for fail!() calls