ChannelGroup Javadoc updated - please review

[Trustin Lee]

Hi folks,

Rather than asking for reviewing a bunch of big Javadoc update, I
decided to ask for your review for each package as early as possible.
(Of course, you can give me feed back for any Netty packages :)

I've just updated Javadoc of org.jboss.netty.channel.group.  Please
let me know if you find any errors or misleading sentences.  An idea
to improve the documentation would be appreciated, too.  Check it out
here:

  * http://www.jboss.org/file-access/default/members/netty/freezone/api/3.1/org/jboss/netty/channel/group/package-summary.html

While you review my work, I will move on to other packages.  Please
keep posting what you want to see in the Javadoc!

Thanks in advance,

— Trustin Lee, http://gleamynode.net/