Xtrack version 0.38.0

Changes:

• Introduce non-linear fringe effects in DipoleEdge element (can be enabled using Line.configure_bend_model(edge='full'))
• Introduce "compound elements" in Line.
  • Elements within compounds can be grouped in twiss using the option group_compound_elements=True
• Rename Bend.method into Bend. model.

Full Changelog: v0.37.2...v0.38.0