GitLab

1. Updated Kea guide to note that removing the hooks-libraries
   configuration element does not always have the expected effect.
2. Moved some documentation from the dhcp_parsers.cc file to the .h file.
3. Expanded checking of the contents of the hooks-libraries configuration
   element.

As some incompatible changes have already been made to the hooks
interface (removal of the setSkip method), it seems pointless to
support both old and new hoos-libraries syntax.  These modifications
remove support for the old syntax.

Modify the tests of the hooks-libraries syntax to allow testing
of both the old and the new syntax.

    Merged in branch 'trac3969'