code: public NewChunk asciiLStrip(NewChunk nc, String chars) {
      SetOfBytes set = new SetOfBytes(chars);
      //update offsets and byte array
      for(int i=0; i < _len; i++) {
        int off = intAt(i);
        if (off != NA) {
          while (set.contains(byteAt(off))) off++;
          int len = lengthAtOffset(off);
          nc.addStr(new BufferedString(_mem, _valstart+off, len));
        } else nc.addNA();
      }
      return nc;
    }
docs: Optimized lstrip() & rstrip() methods to operate across the entire CStrChunk buffer in one pass.
  
  NewChunk is the same size as the original, despite trimming.
  
  @param nc NewChunk to be filled with strip version of strings in this chunk
  @param chars chars to strip, treated as ASCII
  @return Filled NewChunk