fix accuracy for pandas.MultiIndex fixes #84

[mayerantoine]

This fix allow the accuracy function to accept a pandas.MultiIndex as mentioned in the docs i.e (When the argument is a pandas.MultiIndex, the length of the index is used)

[codecov]

Codecov Report

Merging #109 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #109      +/-   ##
==========================================
+ Coverage   76.84%   76.86%   +0.01%     
==========================================
  Files          33       33              
  Lines        2354     2356       +2     
  Branches      379      380       +1     
==========================================
+ Hits         1809     1811       +2     
  Misses        415      415              
  Partials      130      130

Impacted Files	Coverage Δ
recordlinkage/measures.py	89.52% <100%> (+0.2%)	⬆️

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[J535D165]

Thanks for fixing this. Can you do the same for confusion_matrix (before tn = true_negatives(links_true, links_pred, total)) and specificity as well?

[J535D165]

Thanks a lot for your involvement in the project!

(btw tests fail due to an upstream problem with flake)