Add Paratext/USFM processing tutorial

[ddaspit]

• replace "strip_all_text" and "prefer_existing_text" parameters with a single enum parameter

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This change is 

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.12%. Comparing base (b7c06c8) to head (3468ae6).

Files with missing lines	Patch %	Lines
tests/corpora/test_usfm_manual.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #130   +/-   ##
=======================================
  Coverage   88.12%   88.12%           
=======================================
  Files         273      273           
  Lines       16030    16034    +4     
=======================================
+ Hits        14126    14130    +4     
  Misses       1904     1904           

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[johnml1135]

Reviewed 7 of 7 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ddaspit)