Allow arbitrary rolling sizes

[nils-braun]

Fixing #765

[codecov-io]

Codecov Report

Merging #766 into main will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #766   +/-   ##
=======================================
  Coverage   95.89%   95.90%           
=======================================
  Files          18       18           
  Lines        1729     1732    +3     
  Branches      331      332    +1     
=======================================
+ Hits         1658     1661    +3     
  Misses         35       35           
  Partials       36       36           

Impacted Files	Coverage Δ
tsfresh/utilities/dataframe_functions.py	96.77% <100.00%> (+0.05%)	⬆️

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