Add experimental memarray replacement.
- charstar.get(string, offset) gets a pointer to a string
  at the specified (1-based) offset.
- charstar.set(string, offset, value) changes the character
  in a string at (1-based) offset to the numeric byte value.
  Probably evil; charstar.set("ding", 2, string.byte("a"))
  will change *all* occurences of literal "ding" to "dang".