adding -f rst option to compiler (restructured text)

[hemmecke]

The compiler should be able to generate .rst files (restructured text) from the ++ pre- and postdoc documentation.

At the moment there is not clear specification of how pre/postdocs should be formatted. I propose to use ReStructuredText, since it is easily readable in plain text form and one could aim at using sphinx http://sphinx-doc.org/ in order to produce a nice api description of the library. We could even keep that up to date (with every push) by using the http://readthedocs.org service.

Requirement, let the compiler produce appropriate .rst files that generate from something like

foo: A -> B
    ++ blah blah

a .rst file that contains the signature in a human-readable form together with the pre/postoc.

It should be possible to extract such .rst files from the .ao files.

PS: Together with MathJax one would be allowed to use mathematical text inside special rst constructs, like math:'...'

PPS: Maybe we can learn a lot from the Sage community.