API improvements

I noticed we had different ocp-indent configurations I thus added an `.ocp-indent` file, feel free to change it to what you see fit.

I added the `File` and `Dir` components (their implementation may not be correct, I'm not sure I fully understand yet all the base functions of Component and there's no translation in the Makefile). 

But `File` may already be deprecated, I didn't look into `Gen` yet, but I have the impression that `File` is just a special case of `Gen` no ? So if we refactor `Gen` a little bit and make it more general we may express `File` using it (and maybe define an Assemblage.file as a shortcut). It's a good idea to try to keep the number components low, what do you think ?