change the sensitivity function to be always at airmass 1.0

[cylammarco]

Discussed in #115

^{Originally posted by rjs3273 April 6, 2023}
The docs say current dev version of the atmospheric extinction correction only works when provided a science and a standard together. I looked through the code and I think the algorithm is currently moving the science target to the same airmass as the standard observation. That is as opposed to the alternative strategy of moving both to airmass=1 or 0 or any known value. The standard is not modified, only the target. Is that right?

I presume the idea is that atmospheric corrections are rather poorly defined at the best of times so you want to keep the correction applied as small as possible. I can see sense in that.
irrelevent.

This is the second (and independent) source mentioning this issue. I suppose from a data validation point of view, it is far better to compare spectra at airmass 1.0. I will change the workflow for v0.5.X.