Added links to ACL2-Doc, thanks to feedback from J.

Updated documentation for ACL2-Doc browser, based on change of
  control-x a a
to
  control-t g
and the addition of these (as explained in :doc acl2-doc):
  control-t G
  control-t control-t G
I've eliminated using the "control-x a" prefix because it's "owned" by
the "abbrev" mechanism, and I'm concerned that some day Emacs will
take over "control-x a a".  For now, control-x a a prints a helpful
error message, but I plan to remove this key binding after the next
release.



git-svn-id: http://acl2-devel.googlecode.com/svn/trunk@1191 5d84a466-a78b-0930-a311-59b22171a541

Improved the ACL2-Doc "i" (index) command so that if you just hit
<RETURN>, then you go to the index buffer, which now is read-only and
is in ACL2-Doc mode (so that, for example, you can hit <RETURN> while
standing on a topic in order to be taken to that topic).

Cleaned up comments a bit in emacs/acl2-doc.el, in particular,
avoiding going past column 60 in documentation strings, as per
http://www.gnu.org/software/emacs/manual/html_node/elisp/Documentation-Tips.html#Documentation-Tips.


git-svn-id: http://acl2-devel.googlecode.com/svn/trunk@1192 5d84a466-a78b-0930-a311-59b22171a541