ENH: Allow listpri filtering with priority ranges.

So far, the listpri action only supports a single priority. Allowing priority ranges (e.g. todo.sh listpri A-C @work) is a simple but useful enhancement.

Note: The syntax extension only clashes with the [TERM] filtering in a few corner cases, and this can be worked around (e.g. "todo.sh listpri A-Z A-Z" lists all prioritized tasks containing the text A-Z).

todo.sh

@@ -826,7 +826,7 @@ _format()
             {
                 if (match($0, /^[0-9]+ x /)) {
                     print highlight("COLOR_DONE") $0 highlight("DEFAULT")
-                } else if (match($0, /^[0-9]+ \([A-Z]\) /)) {
+                } else if (match($0, /^[0-9]+ \([A-Z]\)[[:space:]]/)) {
                     clr = highlight("PRI_" substr($0, RSTART + RLENGTH - 3, 1))
                     print \
                         (clr ? clr : highlight("PRI_X")) \