function addLineNumbers(src, lineOffset) {
    lineOffset = lineOffset || 0;
    ++lineOffset;

    return src.split("\n").map(function(line, ndx) {
      return (ndx + lineOffset) + ": " + line;
    }).join("\n");
  }
Error Callback
@callback ErrorCallback
@param {string} msg error message.
@param {number} [lineOffset] amount to add to line number
@memberOf module:twgl