Fix/xml escape

partial fixes for #24 

- escape some XML when writing mzXML and mzML
- try to fix the worst offenders
- test for some attributes in mzML
good point, however my reasoning was first and foremost to write valid XML. So with this goal, it seemed best to escape user-supplied (or potentially user-supplied) in a very general basis strings. I think that CV term names fall under this category since they are read from a file during runtime, so potentially a user could supply them,