Add a hook to allow for different renderings of the README files

This is a simple, awesome, useful module.

It would be great to add a hook or some integration mechanism to the module_instructions_show() function so the README file could be rendered in different ways, for example as Markdown or some other format. The thinking is that other modules could intercept the rendering and introduce logic based on thinks like the file suffix to determine how to render the file as opposed to just outputting plain test. This would allow for GitHub-like functionality, which I think could be very useful.

I am aware that this feature request is at odds with the standard module documentation guidelines, but I thought I would raise the issue anyways.

Thanks for a useful little module,
Chris