Updated measurement ton label to match the standard name "measurement_ton".
Fixed issue in MeasureFormat.getInstance().
Modified ParsePosition to make index a property.
Added tests for unit converters.
Extract DefaultFormat and ASCIIFormat from UnitFormat and added UnitFormatTest.
Corrected valid identifier test case.
Updated to throw ParseError for actual parse errors instead of a generic Error.
Updated comments.
Implemented Amount.