Feature/scans methods

[granrothge]

Add methods for:
1 apply a function to a column in each scan of a collection and return the result
2 find the minimum of a column in each scan of a collection and return the result
3 find the minimum of a column in each scan of a collection and return the result
4 find the mean of a column in each scan of a collection and return the result

tests were also added for 2 and 3 which implicitly tests 1

[codecov-io]

Codecov Report

Merging #105 into master will increase coverage by 0.25%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #105      +/-   ##
=========================================
+ Coverage   84.14%   84.4%   +0.25%     
=========================================
  Files          47      48       +1     
  Lines        3886    3937      +51     
=========================================
+ Hits         3270    3323      +53     
+ Misses        616     614       -2

Impacted Files	Coverage Δ
neutronpy/lsfit/plot.py	100% <100%> (ø)
neutronpy/data/scans.py	90.9% <100%> (+1.16%)	✅
neutronpy/lsfit/fitter.py	75.36% <100%> (+1.11%)	✅

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