1.0.4rc1: Merge pull request #831 from lmfit/calc_dely_components

[newville]

Version 1.0.4rc1

New features:

• add calculation of dely for model components of composite models (Issue uncertainties are not easily calculated for components of composite models #761; PR add evaluation of dely for components of composite models #826)
• add R^2 rsquared statistic to fit outputs and reports for Model fits (Issue Extending the fit statistic by including the R2-Statistic #803; PR add R^2 statistic for Model #810)
• add SplineModel (PR Spline model #804)
• add Pearson4Model (@lellid; PR Add Pearson4 fit model (original Wikipedia version) #800)

Bug fixes/enhancements:

• make sure variable spercent is always defined in params_html_table functions (reported by @MySlientWind; Issue Raise UnboundLocalError: local variable 'spercent' referenced before 'assignment' when use method='emcee' and first parameter has vary=False #768, PR FIX: make sure spercent is defined #770)
• always initialize the variables success and covar the MinimizerResult (reported by Marc W. Pound; PR ENH: initialize a few more MinimizerResult attributes #771)
• build package following PEP517/PEP518; use pyproject.toml and setup.cfg; leave setup.py for now (PR BLD: use PEP517/PEP518 #777)
• components used to create a CompositeModel can now have different independent variables (@Julian-Hochhaus; Discussion How to handle different independent variables in CompositeModel? #787; PR enabled use of different independent_vars...  #788))
• fixed function definition for StepModel(form='linear'), was not consistent with the other ones. (@matpompili; PR Fix linear StepModel, wrong function definition #794)
• fixed height factor for Gaussian2dModel, was not correct. (@matpompili; PR Fixed height factor for Gaussian2dModel #795)
• for covariances with negative diagonal elements, we set the covariance to None (PR Draft: Improve handling of covariance calculation #813)
• fixed linear mode for RectangleModel (@arunpersaud; Issue RectangleModule implements 'linear' incorrectly? #815; PR fix 'linear' mode for RectangleModel (lmfit#815) #816)
• report correct initial values for parameters with bounds (Issue Incorrect value in MinimizerResult.init_values #820; PR Correct init_vals #821)
• allow recalculation of confidence intervals (@jagerber48; PR remove if clause blocking recalculation of conf_interval #798)

Deprecations:

• remove support for Python 3.6 which reached EOL on 2021-12-23 (PR drop support for Python 3.6 #790)

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This discussion was created from the release 1.0.4rc1: Merge pull request #831 from lmfit/calc_dely_components.

[newville]

We intend to release version 1.0.4 based on this release candidate in about 1 week.