Dashed slurs are now written as bezier sandwiches, like regular
slurs.
Moved dash-period and dash-fraction from properties for slurs,
phrasingSlurs, and ties. Created new property dash-definition
that contains a list of dash-descriptions for each segment of the
slur.
Defined new ommands \slurHalfDashed and \slurHalfSolid.
Changed bezier-sandwich interface to include thickness parameter
that is used for slurs. This required changes to vaticana=ligature.
Added extract and split to Bezier class.
Adjusted header files to reflect new calling lists.
arpeggio.cc is changed because there is a slur-arpeggio type.