Added support for moving the ACL2 system documentation into the XDOC
system.
**NOTE**: Please do not yet edit these files unless you're me or
          Jared!  I plan to send an announcement about all this soon.

A separate check-in just made to acl2-books (svn revision 2168)
creates a new system/doc/ directory, which provides additional support
for moving the ACL2 system documentation into the XDOC fold.  See
books/system/doc/README.

Note that svn revision 2166 of books/xdoc/preprocess.lisp from the
jared/ branch of acl2-books has not yet been committed to the
acl2-books trunk, as Jared asked me to wait to do that.  However, I
used the updated preprocess.lisp to create new ACL2 source file
doc.lisp.

Here is a summary of some of the major changes.  But note that so far,
none of the ACL2 system documentation has been modified (other than to
convert it to XDOC format, as file books/system/doc/acl2-doc.lisp).
In particular, all of the ACL2 :doc strings are still in the ACL2
source files.  Moreover, code for processing the old-style
documentation strings remains.  J and I will probably remove the
old-style strings and their processing code soon, after we're
reasonably convinced that we will not need to regenerate
books/system/doc/acl2-doc.lisp.

- Changed the definition of the macro DOC, so that :DOC FOO will print
  the documentation from source file doc.lisp, which was copied from
  generated file books/system/doc/rendered-doc.lisp, which was
  extracted from the ACL2 system documentation file (going forward),
  books/system/doc/acl2-doc.lisp.

- Added a macro LEGACY-DOC that functions exactly as DOC had
  previously functioned.

- Added a new source file, doc.lisp.  That file is a copy of generated
  file books/system/doc/rendered-doc.lisp, but unless deliberate steps
  are taken (see the next bullet), doc.lisp will not be overwritten.

- Updated GNUmakefile, in particular modifying the DOC target to
  rebuild the documentation: both books/system/doc/manual/ and source
  file doc.lisp.

Here is a summary of some major remaining things that I plan to do in
order to complete this conversion to XDOC.

- Extend :doc note-6-4 to describe this enhancement.  I'll probably do
  that shortly after this commit, but I'll do it by modifying
  books/system/doc/acl2-doc.lisp, not by modifying (deflabel note-6-4
  ...) in ACL2 source file ld.lisp.

- Copy Lisp comments from release notes into
  books/system/doc/acl2-doc.lisp.

- Write an emacs tool that makes it easy to navigate the text-based
  documentation in doc.lisp.  This will serve as a sort of replacement
  for the Emacs Info version of the documentation.

- Update ACL2 system documentation about the documentation, especially
  topics DOCUMENTATION and DOC.

- Delete legacy code for documentation processing, including some
  files from doc/ as well as source file definitions of MORE,
  SCAN-TO-DOC-STRING-PART, *TERMINAL-MARKUP-TABLE*, and many others.

- Make suitable additional changes to GNUmakefile, for example:
  removing legacy documentation targets; fixing the copy-distribution
  target to avoid copying the TEX manual; and dealing suitably with
  the STATS target (which may also involve changing ACL2 code).


git-svn-id: http://acl2-devel.googlecode.com/svn/trunk@1131 5d84a466-a78b-0930-a311-59b22171a541
More improvements for conversion to xdoc-based documentation.

git-svn-id: http://acl2-devel.googlecode.com/svn/trunk@1132 5d84a466-a78b-0930-a311-59b22171a541