5 undocumented slur.details properties

[Mark Polesky]

Can anyone provide docstrings for these?

These are 5 slur.details properties that are defined in
layout-slur.scm, that are missing from the docstring at the bottom
of slur.cc.

  close-to-edge-length
  encompass-object-range-overshoot
  extra-object-collision-penalty
  slur-tie-extrema-min-distance
  slur-tie-extrema-min-distance-penalty

I'm happy to make a patch, if someone could briefly describe them.

Thanks.
- Mark