add support when fitting PDFs; workaround for plotting recipe with pulls

[marianstahl]

Closes #21

• provide support to nll fitting, as it's done for ennl
• workaround for plotting recipe with pulls (remove margins)
• improve(?) docstrings

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.36%. Comparing base (3a5fae0) to head (46a8af1).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/plotting_recipe.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #24      +/-   ##
==========================================
+ Coverage   68.64%   69.36%   +0.71%     
==========================================
  Files           8        8              
  Lines         236      235       -1     
==========================================
+ Hits          162      163       +1     
+ Misses         74       72       -2     

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[mmikhasenko]

Thanks for fixes!

• I suggest not adding Plots.jl in deps.
• interesting to see that hash of Manifest changes, without anything else changing. Curious, I do not care too much.

Not sure that it's a good idea adding support as an argument. It looks redundant since d<:UnivariantDist has a support(d) method that tells what expected support of the distribution is.

• Totally agree removing margins and mm - that is a quick fix. There must be a better way but I could not figure out quickly.