ttx: pad tags with space if length is less than 4

so that you don't need to do `-t "CFF "` anymore.

Fixes https://github.com/behdad/fonttools/issues/265

Lib/fontTools/ttx.py

@@ -155,6 +155,8 @@ class Options(object):
 			elif option == "-l":
 				self.listTables = True
 			elif option == "-t":
+				# pad with space if table tag length is less than 4
+				value += " " * (4 - len(value))
 				self.onlyTables.append(value)
 			elif option == "-x":
 				self.skipTables.append(value)