* lukas/clean_doc_xmldir/OTP-15190:
  docs: make clean all XMLDIR

This makes it possible to create a custom integration with a
key-value store for example. The key would then point to the
actual address. You would have to write your own epmd module
to make use of that feature.

In order to get line numbers into the ghlink we have to add a post
processing step for all xml files.

This commit also adds a check to see that all files that
are part of an xi:include also have part of XML_FILES
and vice versa. It also fixes any applications where this
was not true.