Flags: version

[steveklabnik]

This issue is part of #125

-V/--version: version information

Using this flag looks like this:

$ rustdoc -V
$ rustdoc --version

This will show rustdoc's version, which will look something
like this:

rustdoc 1.17.0 (56124baa9 2017-04-24)

---

Should we keep this flag or not?

[steveklabnik]

I can't imagine we don't keep this.

[steveklabnik]

Clap has already done this for us!