Added Jared's code for fancy-string-reader, which for example may later prove useful when writing Latex.

The fancy-string-reader mentioned above still needs documentation, but
Jared's book mentioned here in :doc note-7-0, added with his
permission (as is the code itself), helps in understanding it:

  A new reader macro, #{"""..."""}, has been contributed by Jared Davis
  to support the writing of strings without escape characters. See
  his community book books/system/fancy-string-reader-test.lisp for
  examples.

Fixed, I hope, :doc git-quick-start to explain what to do when the
merge fails.