cameo: added "rotate" command

- lang.l, lang.y (rotate): added command "rotate", with cumulative
  rotation
- README: documented "rotate"
- README: corrected typo in description of the translation commands

cameo/lang.l

@@ -49,6 +49,7 @@ NUM	-?[0-9]+\.?[0-9]*
 <INITIAL>optimize		return TOK_OPTIMIZE;
 <INITIAL>remainder		return TOK_REMAINDER;
 <INITIAL>reset			return TOK_RESET;
+<INITIAL>rotate			return TOK_ROTATE;
 <INITIAL>translate		return TOK_TRANSLATE;
 <INITIAL>z			return TOK_Z;