Solve issue #17: Create dom.Node interface

**The changes for this pull request are not finished yet. It is for review purpose only!**

This also includes the following issues:
- #8: Create `dom.Error` interface
- #9: Create `dom.ErrorHandler` interface
- #18: Create `dom.NodeList` interface
- #14: Create `dom.Locator` interface
- #22: Create `dom.UserDataHandler` interface