Update to dashed-slur package

Update to dashed-slur package

Eliminate Bezier & arguments to Bezier::subdivide and
replace with Bezier *

Add support for dashed parenthesis arpeggios.

Add error checking for Bezier::extract arguments.

Remove unnecessary {} and clean up comments.

Update convert-ly rule.

Make Bezier::subdivide and Bezier::extract const functions.

Add complex dashed ties to documentation.