Bump version number.

README.md

@@ -1,7 +1,7 @@
 SixtyPical
 ==========
 
-_Version 0.20.  Work-in-progress, everything is subject to change._
+_Version 0.21.  Work-in-progress, everything is subject to change._
 
 **SixtyPical** is a [low-level](#low-level) programming language
 supporting a sophisticated [static analysis](#static-analysis).

bin/sixtypical

@@ -185,7 +185,7 @@ if __name__ == '__main__':
     argparser.add_argument(
         "--version",
         action="version",
-        version="%(prog)s 0.20"
+        version="%(prog)s 0.21"
     )
 
     options, unknown = argparser.parse_known_args(sys.argv[1:])