implement the arbitrary-path fly-scan ptychography algorithm

[yijiang1]

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-26-10-12585&id=386092

Michal's current implementation has very limited use. Need to improve the GPU engine for applications at the APS.

Checkpoints:
Scan positions

• Linear trajectory: perfectly rectangular grid
• Linear trajectory: rectangular grid w. missing scan points
• Linear trajectory: rotated rectangular grid
• Continuous trajectory
• Load external positions

Algorithm:

• Probe initialization
• Mixed-state + arbitrary-path fly-scan
• Constant vs. varying probe intensity
• Position correction
• Variable probe correction
• Online FSC estimation