Update keystrokes used in muse-mode, as well as docs.

Update keystrokes used in muse-mode, as well as docs.

* lisp/muse-mode.el (muse-insert-map): New variable that defines the
  keymap to use when the user wants to insert something into the current
  buffer using `C-c i'.
  (muse-mode-map): Sort keys somewhat.  Remove binding of `C-c C-v' to
  muse-follow-name-at-point, since this is already used for
  muse-browse-result.  Call `muse-insert-thing' on `C-c i', which will
  prompt for the thing to insert.
  (muse-insert-thing): New function that prompts the user for something
  to insert into the current buffer.  It tries to be as friendly as
  possible by catching possible errors with the message "Not inserting
  anything".
  (muse-mode-completions): Rename from `muse-completions', since this is
  what we use in `muse-mode'.
  (muse-mode-current-word): Similarly.  These don't seem to work
  correctly, for unknown reasons.

* muse.texi (Keystroke Summary): Update to include all keystrokes that we
  utilize.
git-archimport-id: mwolson@gnu.org--2006/muse--main--1.0--patch-121