docs: Updated documentation theme and README

[frgfm]

This PR introduces the following modifications:

• adds logo and favicon to the documentation
• updates the documentation theme to furo
• updates README badges
• expanded unittest

[codecov]

Codecov Report

Merging #61 (be88085) into main (5029de0) will increase coverage by 6.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
+ Coverage   88.10%   94.35%   +6.25%     
==========================================
  Files          10       10              
  Lines         656      656              
==========================================
+ Hits          578      619      +41     
+ Misses         78       37      -41     

Impacted Files	Coverage Δ
torchscan/crawler.py	84.32% <0.00%> (+2.23%)	⬆️
torchscan/modules/receptive.py	83.78% <0.00%> (+18.91%)	⬆️
torchscan/utils.py	100.00% <0.00%> (+25.00%)	⬆️