Note on wrapper for sizing

TODO.md

@@ -3,6 +3,10 @@
 
 TODO:
 
+ - consider a lead byte value used to wrap an encoded `Value` in a
+   size-counted wrapper? That way parsers can quickly skip nested
+   structure they're not interested in...
+
  - https://github.com/uwiger/sext
 
  - http://erlang.org/doc/reference_manual/expressions.html#term-comparisons;