QPID-4568: Fixed the TODO list for Ruby.
fixup! QPID-4567: Moved the gem packaging to using a gemspec file.
QPID-4568: Removed the extraneous block at the top of LICENSE

Not sure how that got in there, likely from when the file was copied
from higher up in the repo. It caused rdoc to generate unneeded site so
it was removed.
QPID-4568: Marked all license prologs as not rdoc material in Ruby.

This prevents rdoc from including the prolog as part of the docs for
each class and module.
QPID-4568: Fixed the wording in the ChangeLog.
QPID-4567: Dropped the errors.rb file and special exceptions.

The code will now raise MessagingException instead in error conditions.
Refactored the Session.sender, Session.receiver and Connection.session
methods to no longer raise those exceptions.
QPID-4568: Improved the Ruby rdocs.

Added more detailed examples. Fixed up the rdoc markups to make the docs
more useful to developers. Added a comprehensive example to the
Qpid::Messaging module rdocs.