Add acceptance tests

[thomas-muench]

This PR does not introduce any updates to the code base, but, equally well important, it adds general acceptance tests, which check that the overall performace of the piccr processing is within acceptable limits, and therefore also remains so. These tests are based on evaluating and comparing the overall RMSD values for a piccr processing run performed on three exemplary real Picarro isotope measurement files.

The new tests include three general acceptance tests and one benchmark test:

• the general acceptance tests include
  • testing that the current package implementation of the piccr processing steps performs at least as good as the original but now outdated piccr command line version;
  • testing that the performance for applying the memory correction is better (lower RMSD) than processing without memory correction switched on;
  • testing that the performance for applying a drift correction is at least as good as when using no drift correction (i.e. only applying memory correction and calibrating the data).
• the benchmark test checks that future changes to the code base do not impair the performance of the currently best processing configuration for the three Picarro example files below the current state.

All these new tests are being passed; specifically:

• the current package implementation performs better than the original command line version;
• applying the memory correction is better than leaving it out;
• applying the drift correction is better than only memory-correcting and calibrating the data; here, drift correction method 2 (drift correction via "double-block calibration") performs better than method 1 ("simple drift correction");
• the benchmark test is passed (obviously).

This PR closes #8.

[thomas-muench]

Congratulations @twollnik! Here I finally introduced the acceptance tests which show that your new implementation of the piccr package actually performs better than my old original version. I do not know exactly why this is the case, but anyway, hooray!

[twollnik]

Thats awesome!! :)