Adds attempt decorator

[thepabloaguilar]

Adds attempt decorator

Checklist

• I have double checked that there are no unrelated changes in this pull request (old patches, accidental config files, etc)
• I have created at least one test case for the changes I have made
• I have updated the documentation for the changes I have made
• I have added my changes to the CHANGELOG.md

Related issues

Closes #264

[codecov]

Codecov Report

Merging #1217 (0ad1868) into master (5033f90) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1217   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           79        79           
  Lines         2425      2434    +9     
  Branches       211       211           
=========================================
+ Hits          2425      2434    +9     

Impacted Files	Coverage Δ
returns/result.py	100.00% <100.00%> (ø)

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[sobolevn]

Thanks you! Only minor suggestions.

I've also removed a test file, because doctests are good enough in this case.

[sobolevn]

Great work! Thank you!