Add capybara matchers to element methods

@natritmeyer

This PR enables the use of capybara options at runtime as arguments supplied to the element/section methods.  I updated README.md with documentation for the new feature, and I updated the tests to use the new capybara options.

This resolves item 3 from issue #41.  We are using all 3 of these new features successfully in our testing environment.

Cheers,
Tim