Travis-CI, new jeweler style and RSpec2

Hi,

I'm now trying text-table. It looks cool!
But ruby-1.9.2 is not written in README.

So I've added setting for test on Travis-CI.
To make it work, I've updated rspec, added 
Gemfile to use bundler, and updated jeweler.

Now you can see the test results:
http://travis-ci.org/#!/akm/text-table

Unfortunately 2 tests were failure In ruby-1.8.6 and ruby-1.9.1,
but rspec works well on Travis-CI.

If you pull this request, please replace akm to aptinio in README.rdoc.

After you turn on text-table in your profile page in travis-ci,
Your push to github will kick the test on Travis-CI.
http://about.travis-ci.org/docs/user/getting-started/

Thank you

Takeshi