Parse a color in XML format. Can be #ARGB or #RGB format, colors as byte hex values.
color in Vexflow format #[A]RGB or undefined for invalid xmlColorString
Main CreateSheet: read the next XML Measure and save all data to the given [[SourceMeasure]].
Using this instead of currentMeasure.AbsoluteTimestamp as it isn't set yet
Software like Guitar Pro gives one octave too low, so we need to add one
An InstrumentReader is used during the reading phase to keep parsing new measures from the MusicXML file with the readNextXmlMeasure method.