Get real cover page of books

[benoit74]

Fix #68

Nota:

• encoded_url property is not yet used, but we will need it very soon for Properly render Detailed Licensing pages of libretexts.org #54
• I've added an item to the release checklist as well: Release 0.1.0 #69

[codecov]

Codecov Report

Attention: Patch coverage is 24.24242% with 25 lines in your changes missing coverage. Please review.

Project coverage is 43.86%. Comparing base (71be961) to head (5aaf93f).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
scraper/src/mindtouch2zim/client.py	24.24%	25 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #70      +/-   ##
==========================================
- Coverage   44.01%   43.86%   -0.16%     
==========================================
  Files          15       15              
  Lines         936      953      +17     
  Branches      128      131       +3     
==========================================
+ Hits          412      418       +6     
- Misses        511      522      +11     
  Partials       13       13              

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[rgaudin]

LGTM