libsyntax: Remove the `use foo = bar` syntax from the language in favor
of `use bar as foo`.

Change all uses of `use foo = bar` to `use bar as foo`.

Implements RFC #47.

Closes #16461.

[breaking-change]
Remove 'static analysis'

This has certain implications that are wrong.

Fixes #16299.
auto merge of #16576 : steveklabnik/rust/static_analysis_gate, r=pcwalton

This has certain implications that are wrong.

Fixes #16299.
auto merge of #16575 : pcwalton/rust/import-foo-as-bar, r=aturon

of `use bar as foo`.

Change all uses of `use foo = bar` to `use bar as foo`.

Implements RFC #47.

Closes #16461.

[breaking-change]

r? @aturon
Explain EOF behavior in File.eof().

Fies #16239.
auto merge of #16578 : steveklabnik/rust/gh16239, r=pcwalton

Fies #16239.