Xtrack version 0.57.0

Changes:

• Introduce more compact json format (parameters equal to defaults are not stored)
• Slicing done with slice-elements referring to the parent. Parent element can be updated also after the slicing and slice elements are updated accordingly. As a result no expression is generated when slicing an element.
• Introduced Replica class to have multiple instances of the same element.
• Element lengths and magnet strengths correctly extracted for replicas and slices in Line.attr, Line.get_table() and Line.twiss().
• Introduced shift_x, shift_y and rot_s_rad properties to all elements in order to introduce misalignments.
• Introduced aperture associated to an element. If present, this is taken into account when slicing the element.
• TwissTable.reverse() reverses also the magnet strengths.
• More efficient and general survey (vertical bends are correctly handled).
• Rationalize element insertion (uses slicing capabilities).
• Removed only_markers flag in twiss.
• Removed element compounds (superseded by capabilities described above).

Full Changelog: v0.56.1...v0.57.0