Add X and Y index for detectors

[tritemio]

For large 2-D arrays is may be useful to store the 2-D pixel coordinates instead of a pixel ID.

Possible fields in /photon_data:

• detectors_row, detectors_col
• detectors_x, detectors_y

[tritemio]

How should we handle the detectors_specs in this case?

Would be possible to specify donor and acceptor? probably not

[tritemio]

A solution can be that the pixel ID can be a scalar or a tuple, so that detectors would be a 2D array with a row for each photon. A set of numbers (a, b, c) represents a detector and the exact meaning depends on the kind of measurement (it can be X, Y and Z, or something else).

In detectors_specs donor, acceptor, etc..., we will have a tuple instead of a scalar to identify the detector.

In case of multi-spot, or in general many detectors with same specs, the spec can be a 2D array, using the same convention of one row per detector.

This would be a clean, scalable, approach that does not require to introduce new fields.

[tritemio]

This is now possible in v0.5 using /setup/detectors/positions. See #33.