v0.5.0

• adds namespace, queue, and input to the Workflow model, so that any non-nil values for these will be included in the POST /workflows (StartWorkflow) response as well as any other response that sends back a Workflow.
• renames WorkflowInput to StartWorkflowRequest to avoid confusion with Workflow.Input and to better match NewWorkflowDefinitionRequest
• changes the type of the input from []interface{} to []string
• gives the queue parameter for StartWorkflowRequest objects a default value -- "default" -- that we return when a user doesn't specify a queue
• renames WorkflowDefinition.Revision to WorkflowDefinition.Version