unicode fix and regex improvement

* Bugfix: When returning a child element with unicode content the end tag position was wrong because it was converted before "chunking" the string.
* Shorted regular expressions matching the start tag.
* Added some tests
* Improved the _updatePositions method. Now it only searches a new start or stop tag it's required. Also we raise an ValueError if the tag was not closed properly.
Small changes
* PEP8 conform: Ingoring W602 and ingoring E122 in test cases