Log Message:
py-lmfit: updated to 0.9.12

Version 0.9.12 Release Notes

New features:
- SkewedVoigtModel was added as built-in model
- Parameter uncertainties and correlations are reported for least_squares
- Plotting of complex-valued models is now handled in ModelResult class
- A model's independent variable is allowed to be an object
- Added usersyms to Parameters() initialization to make it easier to add custom \ 
functions and symbols
- the numdifftools package can be used to calculate parameter uncertainties and \ 
correlations for all solvers that do not natively support this
- emcee can now be used as method keyword-argument to Minimizer.minimize and \ 
minimize function, which allows for using emcee in the Model class

(Bug)fixes:
- asteval errors are now flushed after raising
- max_time and evaluation time for ExpressionModel increased to 1 hour
- loading a saved ModelResult now restores all attributes
- development versions of scipy and emcee are now supported
- ModelResult.eval() do no longer overwrite the userkws dictionary
- running the test suite requires pytest only
- improved FWHM calculation for VoigtModel