Setting X-offset and Y-offset graphically.

[Richard Shann]

This is a quick demonstration of tweaking the position of a trill sign
by dragging on the LilyPond pdf image in Denemo:

https://vimeo.com/64131774

Of course, the actual LilyPond text can then be further altered
textually, but this remembers the syntax for you.
I am still not there yet with the designing of slur shapes, but it is on
my list of things to do.
Thanks to Janek Warchoł on the lilypond-devel-request list for
triggering this solution, and Harm for the brilliant red-dot markers.

Richard Shann