[MRG] Update doc and exemples

[rflamary]

Types of changes

• Update readme wity new API
• Add nice image of contributors to readme and contributors.md
• Big update of the examples that can now be in multiple sections

Motivation and context / Related issue

How has this been tested (if it applies)

PR checklist

• I have read the CONTRIBUTING document.
• The documentation is up-to-date with the changes I made (check build artifacts).
• All tests passed, and additional code has been covered with new tests.
• I have added the PR and Issue fix to the RELEASES.md file.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.10%. Comparing base (d2ea084) to head (dc82e14).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #754   +/-   ##
=======================================
  Coverage   97.10%   97.10%           
=======================================
  Files         101      101           
  Lines       20493    20493           
=======================================
  Hits        19900    19900           
  Misses        593      593           

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