Pi digit extraction algorithm (#1996)

* added pi digit extraction formula

* updating DIRECTORY.md

* fixed typo in a comment

* updated bbp_formula.py

* Update maths/bbp_formula.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update maths/bbp_formula.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update bbp_formula.py

* Update and rename bbp_formula.py to bailey_borwein_plouffe.py

* updating DIRECTORY.md

* calculate

* "".join(bailey_borwein_plouffe(i) for i in range(1, 12))

* Update bailey_borwein_plouffe.py

* Update bailey_borwein_plouffe.py

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>