Flag: output format

[steveklabnik]

This issue is part of #125

-w/--output-format: output format

This flag is currently ignored; the idea is that rustdoc would support
various output formats, and you could specify them via this flag.

Rustdoc only supports HTML output, and so this flag is redundant today.

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Should we keep this flag or not?

[steveklabnik]

Given that this is currently ignored, we should probably do so too.

[steveklabnik]

We talked about this at the tools team meeting today and the intention is to remove this flag.

--emit gives the same functionality and is consistent with the compiler.

[steveklabnik]

rust-lang/rust#44136 is the issue tracking the deprecation; it may or may not be removed, but it means we don't need to support it.