Version constructor

Version(int major, int minor, int patch, { String pre, String build })

Creates a new Version object.

Implementation 

factory Version(int major, int minor, int patch, {String pre, String build}) {
  var text = "$major.$minor.$patch";
  if (pre != null) text += "-$pre";
  if (build != null) text += "+$build";

  return new Version._(major, minor, patch, pre, build, text);
}