Update dashed slurs to have variable thickness.

Update dashed slurs to have variable thickness.
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.

Adjusted documentation to reflect changes.