Add .travis.yml, Add a Gemfile (for travis), tweak Rakefile for 1.8.7, set required ruby to 1.8.7, regenerate gemspec in 1.8.7
Update Delay stamp format to XEP-0203 as XEP-0091 has now been marked obsolete

XEP-0091 was last updated 2009-05-27, and it's status is Obsolete

http://xmpp.org/extensions/xep-0203.html
> Implementations that support XEP-0091 should support the protocol defined herein as soon as possible, but should continue to support the protocol defined in XEP-0091 for backwards compatibility until the status of that specification is changed to Obsolete.