support lmoments as a model in the fit_model method

[DirkEilander]

First off all, great work on making this open source package, much appreciated!

Is your feature request related to a problem? Please describe.
It would be a nice addition to support lmoments based estimates of extreme value distribution parameters. "L-moments are more robust than conventional moments to outliers in the data and enable more secure inferences to be made from small samples about an underlying probability distribution" source

Describe the solution you'd like
support lmoments as a model in the fit_model method

Additional context
It could be supported by this package https://github.com/Ouranosinc/lmoments3

[georgebv]

Thank you, there is a discussion about this topic here: #92