Use specified capitalization in Marketo API calls.

- Automatic translation is correct for *most* Marketo API request
  parameter fields, but not all. Ensure that the request objects are
  created properly. Resolves #15.

Also:
- Fixing test/build issues.
  - Removing dead tests.
  - Chasing the rbx moving target. Again.
  - Ruby 1.9.2 (MRI) will no longer be tested on Travis.