Add new magic function GenerateDocumentation
Add three demo invocations of GenerateDocumentation
Improve Create{Main,Title}Page
PackageInfo.g: Add AutoDoc rec

Specify a custom Copyright and extra includes for CreateMainPage.
Add regenerated title.xml and AutoDoc.xml files

This in particular demonstrates how to use the new function for
packages that do not themselves use AutoDoc.
CreateAutomaticDocumentation: make create_full_docu param optional

Also, remove it from the documentation. It (and also the already
undocumented 'entities' argument) are only kept around for
backward compatibility.
Switch GenDocs to modern Create{Title,Main}Page
Reduce some minor code duplication