Proof of concept: Add support for customizing GAPDoc <TitlePage>

The code now also indents the generated output nicely, hopefully
further reducing the need to manually edit it.
Merge pull request #7 from fingolfin/title-xml-hack

Proof of concept: Add support for customizing GAPDoc <TitlePage>
Added Max Horn as author.
Removed comments and custom banner in pkgInfo.
Hopefully got rid of those annoying \