TRestFitAnalysisProcess needs to be implemented

[jgalan]

We are missing a generic process that just takes in the configuration file an observable from the analysis tree to be the target of the fit and define a fit function, range and parameter hints and limits.

The process should store the results of the fit.

This process could be handy when for example we study the gain evolution of a particular dataset from the detector real data. We could for instance use this process to get the position of a particular calibration peak found at a given observable.

We could have something as ...

<TRestFitAnalysisProcess>

    <fit observable="hitsAna_energy" func="gaus" range="(100,400)" initParam=.... limitParam=..../>
    <fit observable="rawAna_thresholdIntegral" func="[0] + [1]*x + [2]*TMath::Exp(..." />

</TRestFitAnalysisProcess>