Inline templates

Do we want to add support for inline templates? That is, templates that are defined as strings in the `View` class, and not in a separate file to be read. I think it'd be helpful, and we could also simplify the configuration by not requiring `paths`

What should the API look like?

- Override `def template` and returns a string?
- Add a `template` DSL which takes a string?
- Put at the end of the file after __END__, then use DATA to access it? (A strange idea surely, and could be implemented via the other two if someone wanted to)

Similarly, would we want to allow layouts to be defined inline? I imagine it would be defined in a local base class, and inherited by the children.