Add a rather ugle XmlUnescape because RegExp is VERY SLOW....

New results
From 20+ seconds to 0.64 seconds with this change.
```
unittest-suite-wait-for-done
parse time 0:00:00.647532
PASS: diagram parse visit

All 1 tests passed.
unittest-suite-success
```
Shouldn't all references to _decodeXml be using _XML_UNESCAPE.convert?