pad method
Implementation
String pad(int length, [String chars = ' ']) {
var strLength = length != 0 ? this.length : 0;
if (length == 0 || strLength >= length) {
return this;
}
var mid = (length - strLength) / 2;
return (_createPadding(mid.floor(), chars) + this + _createPadding(mid.ceil(), chars));
}