Import and use AsciiDoc 7.1.2 configuration files

Import and use AsciiDoc 7.1.2 configuration files

In the past, we have hit annoying incompatibilities when
people have attempted to rebuild ELinks documentation
with new versions of AsciiDoc:

http://bugzilla.elinks.cz/show_bug.cgi?id=989
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=491820

So now we bundle the configuration files from a known good version
to let ELinks documentation be built with them regardless of which
version has been installed on the machine.