Restored from old commit
Write to XML supported
Read from XML supported
Write to XML implemented
Write to XML implemented
Write to XML implemented
Write to XML and type implemented
Duplicated XML constants removed
Duplicated XML constants removed
Write to XML dummy implementation
Duplicated XML constants removed
Fix issue #26
Exception type changed to ParseException
Created a keyboard for the variables

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
MathSymbolEditor now supports variables

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Merge remote-tracking branch 'folkert/work' into work