Toward working emitter tests

Work in progress.

- To ease integration I want to provide a large code layout change of Emitter in a timely manner.
- The CompareOriginalAndEmittedText method skips the start and end mark which made one test pass
- I've added new tests in advance of the corresponding fixes to Emitter.

The new tests tries to home in on how I think the emitter should behave when rendering the document start events. @aaubry, please give feedback on these tests.