[ruby-core:54196] Encouraging use of CommonRuby

I think we need to do more to encourage the use of the CommonRuby
project in bugs.ruby-lang.org.

There are currently 429 "feature" issues open in ruby-trunk. The
majority of these would affect all Ruby implementations, and are not
specific to MRI. I believe ruby-trunk should only house bugs and
features that are specific to MRI (or at least, they initially seem to
apply only to MRI).

What can we do to encourage folks to use CommonRuby more?

* A top-level link for CommonRuby that clearly states any new
user-visible Ruby language/library features (or feature changes)
should be filed here.
* Migrate existing feature requests to CommonRuby if they apply to
other Ruby implementations.
* A period of auditing feature requests filed against ruby-trunk and
other projects, migrating them to CommonRuby or recommending re-filing
in CommonRuby.

Encouraging use of CommonRuby would do a lot to show that the
implementations are collaborating on the future of Ruby, and it would
help us implementers filter out MRI-specific bugs/features from those
that will affect our implementations.

Thoughts?

- Charlie