Take into account non-parallel crystal mesh for Crystal class

[Didou09]

Objective:

• On branch Issue202, the CrystalBragg class handles spherical crystals, but it does not handle non-parallelism.
• The following functions should exist in a version taking into account non-paralelism:

  tf.geom._comp_optics.calc_dthetapsiphi_from_lambpts()
  tf.geom._comp_optics.CrystBragg_get_noute1e2_from_psitheta()
  tf.geom._comp_optics.calc_xixj_from_braggphi()
  tf.geom._comp_optics.calc_braggphi_from_xixjpts()

• In order to understand the logic, you should retrace the code for the user's point of view, make sure all steps are clean and operational.

Necessary steps:

• Propose a solution to store 2 angles and / or a 3-unit vector basis for the mesh in the CrystalBragg class.
• The 2 angles refer to the 2 local (geometrical) vectors (e1, e2).
• Check all methods in the class from section (l. 1000):

  # -----------------
  # methods for surface and contour sampling
  # -----------------

[Didou09]

@adriendaros , the commands you're looking for are:

In [44]: det = dict(np.load('inputs_temp/det37_CTVD_incC4_New.npz', allow_pickle=True))

In [45]: cryst = tf.load('inputs_temp/TFG_CrystalBragg_ExpWEST_DgXICS_ArXVII_sh00000_Vers1.4.9-315-gc93fa7a3.npz')
Loaded from:
    /home/didier/Documents/Projects/tofu/inputs_temp/TFG_CrystalBragg_ExpWEST_DgXICS_ArXVII_sh00000_Vers1.4.9-315-gc93fa7a3.npz

In [46]: pts0, vect = cryst.get_rays_from_cryst(phi=np.pi, returnas='(pts, vect)')

In [47]: pts = pts0 + np.r_[1, 3,5, 7][None, :]*vect[:, :, 0]

In [48]: cryst.plot(pts=pts, det=det)