Fix documentation mistake
Replace magic variable with qq argument

After feedback on the mailing list, I've abandoned the magic variable
in favor of a quasiquoter argument.  This also works better with
singleton checking.

Closes #1
Mention semantic versioning
Remove text about false singleton warnings

As of version 6.5.1, SWI Prolog correctly recognizes variables inside
of quasiquotations.
Prepare for release