[plt-scheme] Scribble syntax documentation

I've made considerable changes to the beginning part of the reader
documentation.  See the new text at

  http://docs.plt-scheme.org/scribble/reader.html

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                  http://www.barzilay.org/                 Maze is Life!