Update information regarding mailing lists

[stomar]

The mailing list software changed to GNU Mailman, so that the subscribe / unsubscribe information is not up-to-date.

[stomar]

I updated the *-request addresses etc.

However, I think there still should be some restructuring of these pages (mailing-lists and mailing-lists/manual-instructions), to better reflect the 3 possibilities: "our" simple form, web interface with more options (password, digest, ...), basic email commands.

Also missing: hint to more lists on lists.ruby-lang.org

Thinking about it...