Including def-gl-rule, which support xdoc,
local, and disabledp inside gl.lisp.

Note: I seem to remember that I had some second thoughts about the
  name disabledp.  If anyone has comments on that, please open an
  issue filed against me.
Adding a couple notes to the book release notes.
Fixing a typo
Merge pull request #254 from ragerdl/master

3 CLs