gof (pvalue), fwhm uncertainty, iterative fit, mc energy spec for test fit

[LisaSchlueter]

• gof: pvalue based on beast-squares (baseline), likelihood ratio, MC
• fwhm with correlated uncertainties
• iterative fit in case cov mat not semi positive definite
• function to find nearest semi positive definite cov mat
• MC test data (energy spectrum based on randomized model function)

[codecov]

Codecov Report

Attention: 43 lines in your changes are missing coverage. Please review.

Comparison is base (2a96714) 0.19% compared to head (041fd42) 18.29%.

Files	Patch %	Lines
src/gof.jl	35.71%	36 Missing ⚠️
src/specfit.jl	72.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             dev      #32       +/-   ##
==========================================
+ Coverage   0.19%   18.29%   +18.10%     
==========================================
  Files         19       21        +2     
  Lines       1052     1159      +107     
==========================================
+ Hits           2      212      +210     
+ Misses      1050      947      -103     

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