Fix indentation of output

[bsvh]

This adds a customization variable mugur-indentation which defines what a single level of indentation it. It then indents the output according to that. It defaults to two spaces. It also removes leading spaces in config.h and rules.mk.

[mihaiolteanu]

It removes the leading spaces in config.h, that's nice, but it also removes them in the elisp code, which I don't like.

I think it comes down to "Do I want the elisp to be clear or do I want the generated code to be clear?"
I think I prefer the former, as of now.