[subset] Accept unicode ranges

Eg --unicodes=41-5a,61-7a to choose ASCII letters.  Note that with
this, --unicodes-file accepts fontconfig .orth files that do not
include other files.

Lib/fontTools/subset.py

@@ -2428,7 +2428,15 @@ def parse_unicodes(s):
   import re
   s = re.sub (r"0[xX]", " ", s)
   s = re.sub (r"[<+>,;&#\\xXuU\n  ]", " ", s)
-  return [int (x, 16) for x in s.split (' ') if len (x)]
+  l = []
+  for item in s.split():
+    fields = item.split('-')
+    if len(fields) == 1:
+      l.append(int(item, 16))
+    else:
+      start,end = fields
+      l.extend(range(int(start, 16), int(end, 16)+1))
+  return l
 
 def main(args):