add ladspa ugen + few other changes

[defaultxr]

Here are the changes in this PR:

• add ladspa UGen (from sc3-plugins)
• fix destructuring-bind handling in convert-code
• fix get-synthdef-metadata so it returns information correctly when its argument is a node
• add cl-patterns contrib link. cl-patterns is my sequencing/patterns library that supports using cl-collider as its audio backend.