Implemented HitRate for IR

[lucadiliello]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Fixes #571 .

PR review

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[codecov]

Codecov Report

Merging #576 (f4472df) into master (3984ccd) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #576   +/-   ##
=====================================
  Coverage      95%    95%           
=====================================
  Files         142    144    +2     
  Lines        5004   5033   +29     
=====================================
+ Hits         4759   4788   +29     
  Misses        245    245           

[SkafteNicki]

Just a few comments, PR already great :]
Remember to add an entry in the changelog.

[Borda]

LGTM

[lucadiliello]

I've improved the documentation for all the retrieval metrics since many improvements applied also to the other metrics.