Add avy-action-ispell to avy.el

The point should return to its starting location after the desired word
is corrected. As is the case for the other avy-action-{something}
functions, this function is also added to the avy-dispatch-alist.

Fixes #142

avy.el

@@ -523,6 +523,17 @@ Set `avy-style' according to COMMMAND as well."
    (just-one-space))
   (message "Killed: %s" (current-kill 0)))
 
+(defun avy-action-ispell (pt)
+  "Auto correct word at PT."
+  (save-excursion
+    (goto-char pt)
+    (if (looking-at-p "\\b")
+        (ispell-word)
+      (progn
+        (backward-word)
+        (when (looking-at-p "\\b")
+          (ispell-word))))))
+
 (defun avy--process (candidates overlay-fn)
   "Select one of CANDIDATES using `avy-read'.
 Use OVERLAY-FN to visualize the decision overlay."