feat: Added Distance-IoU and Complete IoU

[frgfm]

This PR aims at:

• introducing the ops module
• adding implementations of distance iou and complete iou losses
• adding corresponding tests
• adding corresponding docs

[codecov]

Codecov Report

Merging #12 into master will increase coverage by 2.47%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #12      +/-   ##
==========================================
+ Coverage   51.85%   54.32%   +2.47%     
==========================================
  Files          15       17       +2     
  Lines         702      740      +38     
==========================================
+ Hits          364      402      +38     
  Misses        338      338

Impacted Files	Coverage Δ
holocron/ops/boxes.py	100% <100%> (ø)
holocron/ops/__init__.py	100% <100%> (ø)