Refactor

[moi15moi]

A big refactor is needed to close #2 and #3.

For the moment, I only edited the Algorithm conversion explanation.md doc.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 98.83811% with 15 lines in your changes missing coverage. Please review.

Project coverage is 97.35%. Comparing base (683a8b4) to head (8efb844).

Files with missing lines	Patch %	Lines
video_timestamps/abc_timestamps.py	91.89%	6 Missing ⚠️
video_timestamps/video_timestamps.py	96.18%	5 Missing ⚠️
video_timestamps/fps_timestamps.py	97.18%	2 Missing ⚠️
video_timestamps/rounding_method.py	88.88%	1 Missing ⚠️
video_timestamps/text_file_timestamps.py	95.45%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main       #4      +/-   ##
==========================================
+ Coverage   94.83%   97.35%   +2.52%     
==========================================
  Files          17       16       -1     
  Lines         949     1438     +489     
==========================================
+ Hits          900     1400     +500     
+ Misses         49       38      -11     

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[moi15moi]

Actually, I just realised that since $$pts_time \in \mathbb{Q}^{+}$$, I could use Fraction instead of int.
With this change, we could support any unit.