Changes in QMBCFN 1.70:
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- new file types allowing fast repeated fits for multiple data samples (see user manual for details)
- new option allowing an arbitrary function of the parameters to be added to chi^2 (see user manual for details)
- Bayesian constraints are now disabled by default
- numerical differentiation for first derivatives is now enabled by default
- fixed bug in the GUI concerning the hiding/showing of the lineedit fields for the derivatives
- fixed typos in error messages