Add GetCase command to get a single case by ID
Add Travis configuration
Use reflection to avoid awkward getDirectory()

Reflection can provide the directory that the concrete child class of an
abstract class is defined in.
Avoid GitHub rate limiting Travis composer install
Add Travis build status badge to README
Increase error_reporting() to maximum during tests
Allow setting multiple parameters in OperationTest
Make "id" required for GetCase operation
Allow non-numeric external_id in GetCase operation
Add getCaseStatus() to convert between IDs/names
Fix PreValidator setting non-set query params
Add client() method, gets OperationTestCase client
Add network test for GetCases operation
Remove redundant "numeric" from string types

Guzzle does this conversion internally, so when you say a parameter
should be a string, it also accepts numeric types.
Add GetCase system test