Pre-1.0 changes

std`std` facade

We should revisit some APIs in libstd`libstd` now that the facade effort is complete.

For example, the treatment of environment variables in the new Command`Command` API is waiting on access to hashtables before being approved.

Trait reform

Potential for standard conversion traits (to`to,`, into`into,`, as`as`).

Probably many other opportunities here.

Unboxed closures