Improve documentation

[shunichironomura]

• add poetry and ruff badges
• add gen_index.py
• remove index.md
• configure gen-files scripts
• Add linebreak
• add gen_index_page to gen_pages.py
• rename callback to build
• update command.md
• Update documentation for contexts/watchers/reporters
• remove unnecessary import
• change links
• export CapsuleParams
• add extending.md
• add deploy-docs to release workflow

[codecov]

Codecov Report

Attention: Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.

Project coverage is 78.71%. Comparing base (3b4f510) to head (4c8c7f5).
Report is 1 commits behind head on main.

Files	Patch %	Lines
capsula/_capsule.py	0.00%	2 Missing ⚠️
capsula/_reporter/_base.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #262   +/-   ##
=======================================
  Coverage   78.71%   78.71%           
=======================================
  Files          29       29           
  Lines         996      996           
=======================================
  Hits          784      784           
  Misses        212      212           

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