fixing unit issue in Shkl. Units are now in degrees and correctly scaled to be additive with U and Y respectively.

[saransh13]

The anisotropic peak broadening model is based on paper Peter W. Stephens, Phenomenological model of anisotropic peak broadening in powder diffraction, J. Appl. Cryst. (1999). 32, 281-289. The peak broadening terms are computed in the units of radians (see below).

However, all peak broadening terms in the wppf module is in units of degrees. There is an additional scale term of 1E4 in the gaussian broadening and 1E2 in Lorentzian broadening to be consistent with GSAS. Adding these scale factors so that S_hkl are now in the units of degrees nm^-4.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.01%. Comparing base (97d9bd2) to head (c02a681).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
hexrd/powder/wppf/peakfunctions.py	0.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #850      +/-   ##
==========================================
- Coverage   56.01%   56.01%   -0.01%     
==========================================
  Files         143      143              
  Lines       22017    22019       +2     
==========================================
  Hits        12333    12333              
- Misses       9684     9686       +2     

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