add centroided mzXML and mzML test files
adjust test cases to centroided mzXML and mzML files
allow .parseMzMl to read centroided data
Merge branch 'master' into centroided
add .createMassObject helper function
.importMzXml and .importMzMl use .createMassOjbect now
add centroided support for all import* functions; closes #11