Merge pull request #507 from takluyver/prompt-manager Prompt manager refactoring: use a new `PromptManager` class responsible for handling everything to do with the prompts. The critical part is its `render` method, which assembles the necessary information, then uses the string formatting introduced in Python 2.6 to fill in the prompt template. I've expanded the definition of 'prompts' to include the auto_rewrite prompt (`"------> "` by default). So there are now four prompts: input, continuation, output, and rewrite. This definition of prompts does not include input/output separators. For now, I've left those as attributes of the main InteractiveShell object.