Draft: Resolve "Alignment: focus calibration is missing some of the original features"

The focus.m function presents more options than the simple 'std' merit function.

Mandatory features:

• Implement PSD method
  • Implement simple azimuthal integration function
  • Implement averaging logic in frequency domain
• Create unit tests
• Add documentation

Optional features:

• Implement additional methods:
  • Gradient
  • Edge

Closes #155.