BUG: completion of task number didn't remove add date.

Need to make match of preceding priority optional.
Also tighten patterns for priority and done marker by anchoring them to the front, as the leading task number has already been substituted away.

todo_completion

@@ -58,8 +58,8 @@ _todo()
                             # a safety check of the ls action output.
                             local todo=$( \
                                 eval TODOTXT_VERBOSE=0 $_todo_sh '-@ -+ -p -x command ls "^ *${cur} "' | \
-                                sed -e 's/^ *[0-9]\{1,\} //' -e 's/\((.) \)[0-9]\{2,4\}-[0-9]\{2\}-[0-9]\{2\} /\1/' \
-                                    -e 's/\([xX] \)\([0-9]\{2,4\}-[0-9]\{2\}-[0-9]\{2\} \)\{1,2\}/\1/' \
+                                sed -e 's/^ *[0-9]\{1,\} //' -e 's/^\((.) \)\{0,1\}[0-9]\{2,4\}-[0-9]\{2\}-[0-9]\{2\} /\1/' \
+                                    -e 's/^\([xX] \)\([0-9]\{2,4\}-[0-9]\{2\}-[0-9]\{2\} \)\{1,2\}/\1/' \
                                     -e 's/[[:space:]]*$//' \
                                     -e '1q' \
                             )