Xpkg: pack must use create-manually instead of create

In Xamarin's xpkg or xamarin-component.exe, the 'create' command
merely creates a skeleton package, while the command to actually create
the package using the provided arguments and files is 'create-manually'.
Xpkg: inline document options
Xpkg: Add support for missing arguments

Support for the following additional arguments available in the
newer xamarin-component.exe tool (successor of xpkg).

* Publisher Url
* Source Code Repo Url
* Documentation Url
* Screenshots
* Popover image