Using TAB for completion in the minibuffer and compose buffer

This seems to work, but binding some of these variables may not actually be necessary:
```diff
diff --git a/ement-room.el b/ement-room.el
index 0bd1b95..fd74e96 100644
--- a/ement-room.el
+++ b/ement-room.el
@@ -182,6 +182,7 @@ (defvar ement-room-minibuffer-map
(let ((map (make-sparse-keymap)))
(set-keymap-parent map minibuffer-local-map)
(define-key map (kbd "C-c '") #'ement-room-compose-from-minibuffer)
+ (define-key map (kbd "TAB") #'complete-symbol)
map)
"Keymap used in `ement-room-read-string'.")

@@ -2145,7 +2146,9 @@ (defun ement-room-read-string (prompt &optional initial-input history default-va
(setq-local completion-at-point-functions
'(ement-room--complete-members-at-point ement-room--complete-rooms-at-point))
(visual-line-mode 1)
- (run-hooks 'ement-room-read-string-setup-hook))
+ (run-hooks 'ement-room-read-string-setup-hook)
+ (setq-local tab-always-indent 'complete
+ tab-first-completion t))
(read-from-minibuffer prompt initial-input ement-room-minibuffer-map
nil history default-value inherit-input-method))))

@@ -3903,12 +3906,15 @@ (defun ement-room-init-compose-buffer (room session)
(setf ement-room-compose-buffer t)
(setq-local completion-at-point-functions
(append '(ement-room--complete-members-at-point ement-room--complete-rooms-at-point)
- completion-at-point-functions))
+ completion-at-point-functions)
+ tab-always-indent 'complete
+ tab-first-completion t)
;; FIXME: Compose with local map?
(use-local-map (if (current-local-map)
(copy-keymap (current-local-map))
(make-sparse-keymap)))
(local-set-key [remap save-buffer] #'ement-room-compose-send)
+ (keymap-set (current-local-map) "TAB" #'indent-for-tab-command)
(setq header-line-format (substitute-command-keys
(format " Press \\[save-buffer] to send message to room (%s)"
(ement-room-display-name room)))))
```