Adding and Refactoring Tests

[TheMetalCode]

I have a project I'm working on where I plan to use this gem to talk to the Infusionsoft API, so I thought I'd be courteous and add some test coverage. I've focused for now on the functions I know I'll use. A few items of particular note:

• The exceptions_test.rb was refactored to avoid overriding the XMLRPC::Client class, since that was interfering with my ability to unit test the client methods. I instead just stubbed the #call method itself, and was still able to successfully test particular types of exceptions.
• Added a .travis.yml for Travis CI. I thought of this specifically because of your stated desire to support particular ruby versions. Travis gives you the ability to test in those versions, for free. Added a Coveralls badge and simplecov as well. Ruby 1.8.7 and REE are excluded from this simply because Simplecov & Coveralls require 1.9.2 or higher.
• I used VCR to stub the API calls. I had my real API credentials in the test_helper config at first but created fake contacts and companies in my Infusionsoft instance to test against, and then I removed all references to my Infusionsoft url and API key. So the stubs represent real web requests that actually happened, but they are doctored a bit just to obscure any PII.

[nateleavitt]

@TheMetalCode Wow! This looks awesome. Give me a couple days to review. I'll comment on here if I have any questions.

[nateleavitt]

Thanks for the contribution!