Draft: pulse capacitors data fitting

This is development branch to develop improved method for AGIPD relative gain correction

An idea of the first stage:

1. Fit pulse capacitors data with hook function:

H(x) = \frac{a}{(x-c)^n}+kx+b

This should better correct nonliearity at the end of transition region

2. Use thresholds closer to the values of gain and use the gap between thresholds as indicator of transition region

g_0 + 4.5\sigma_0 < g < g_1 - 4.5\sigma_1\\

The pulse capacitors data example

The comparison of corrections

@turkot