1.0.0: Breaking changes in the API

This version introduces major changes and breaks backward compatibility.

Here is a list of the changes:

• The import statement now uses openpmd_viewer instead of opmd_viewer, e.g.

from openpmd_viewer import OpenPMDTimeSeries

• For consistency, ts.get_particle now return particle positions in meters,
  instead of microns. For instance, in the code below, x, y, z will be in
  meters

x, y, z = ts.get_particle(['x', 'y', 'z'], iteration=1000)

• In ts.get_field, slicing can now be done in several directions, and for
  1d, 2d, 3d, and circ geometries. As a consequence, this breaks backward
  compatibility for 3d field:
  get_field(field=field, coord=coord, iteration=iteration)
  used to return the central slice along y while it now returns the full 3d field.
  In addition, the name of the argument of get_field that triggers slicing
  has been changed from slicing_dir to slice_across (and slicing has been
  changed to slice_relative_position).
• openPMD-viewer does not rely on Cython anymore. Instead, it uses numba
  for functions that perform a substantial amount of computation.
• A new function (ts.iterate) was introduced in order to quickly apply a
  given function to all iterations of a time series. See the docstring of
  ts.iterate for more information.
• The function get_laser_envelope does not support the argument index anymore
  (which was effectively used in order to perform slicing). Instead, users should use
  the argument slicing_dir. In addition, get_laser_envelope now supports the
  argument plot_range.
• The function get_laser_waist does not support the agument slicing_dir anymore.