[Haddock] vim help text export

[Simon Hengel]

>   * Should the file contain *everything* or should users combine it
> with information from .hi files?
>     For example, should we put declarations in the file or should
> users recover them from .hi files?

I think it would be convenient to get everything needed to produce the
HTML docs from the Haddock API.

BTW: Does reading the .hi files involve GHC's static flags?

>   * Should it be a text file or a binary file? (I.e. should we invent
> a new format or should it be the .haddock file).

I'd put all effort into the API.  If we provide text files as a "second
API", then you get parse error when things change.  If you use the API,
the type checker will help you on API changes.