Enable that location and scale parameters might be set or not used.

[veni-vidi-vici-dormivi]

Some distributions do not use loc and scale. While all distributions have loc as parameter, for some it might make sense to set it to 0 like the beta distribution or even just if one has calculated residuals for their data and knows the loc is 0. Thus, I implemented an option to set the location in the expression to a certain value (note because of #525 it can only be ints atm). Moreover, the discrete distributions tend to not have a scale parameter so I made it optional.

• Tests added
• Fully documented, including CHANGELOG.rst

[veni-vidi-vici-dormivi]

Test for discrete distributions that actually omit the scale parameter follow in another PR as they also need some other changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.13%. Comparing base (4ef7a1f) to head (f252fda).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #597      +/-   ##
==========================================
+ Coverage   80.12%   80.13%   +0.01%     
==========================================
  Files          49       49              
  Lines        3064     3066       +2     
==========================================
+ Hits         2455     2457       +2     
  Misses        609      609              

Flag	Coverage Δ
unittests	80.13% <100.00%> (+0.01%)	⬆️

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[mathause]

Looks good.

[yquilcaille]

I think that the modifications done make sense. I simply suggest to add for the location (line 1039) the logic used for the scale with the try / except (line 1060-1062).