4-th order polynomial background

[stestoll]

Some recent RIDME papers (Wort et al Appl.Magn.Reson. 2023 https://doi.org/10.1016/j.jmr.2023.107460 and Abdullin et al Appl.Magn.Reson. 2022 https://doi.org/10.1007/s00723-021-01326-1) used a 4th-order polynomial as a background model.

Maybe add this model to DeerLab, or provide an analysis example where this background model is user defined.