Added content type footnotes+xml so mail merge fields are supported

[402Martin]

1. Added a 1 line change on CONTENT_TYPES, that allows the replacing of a mail-merge field on the footnotes of a docx.

Description

1. Added a 1 line change on CONTENT_TYPES, that allows the replacing of a mail-merge field on the footnotes of a docx. "application/vnd.openxmlformats-officedocument.wordprocessingml.footnotes+xml",

Motivation and Context

Thes change allows for the merge of fields inside footnotes.

How Has This Been Tested?

1. Created a small testing script:

   from io import BytesIO
   from mailmerge import MailMerge
   
   def mergeDocumentToLocalFile(templatePath, outputPath, mergeFields):
     print(f"Using template - {templatePath}")
     with open(templatePath, "rb") as file:
         template = file.read()
     buffer = BytesIO(template)
     with MailMerge(buffer) as document:
         document.merge(**mergeFields)
         output_filelike = BytesIO()
         document.write(output_filelike)
         # need to reset the stream before writing to file
         output_filelike.seek(0)
         with open(outputPath, "wb") as output_file:
             output_file.write(output_filelike.read())
         print("File saved to", outputPath)

2. Used multiple documents to test with and without footnotes.
3. Run the script with multiple documents

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

[iulica]

Thanks for the fix. I will add it as it is, but I would have liked a test file and test script in the tests/ folder so it could be tested.

[iulica]

well, did you test it ? I get 10 unittest errors. I reverted it as it will probably give errors to existing documents.

[iulica]

Post it as an issue with an example docx and I will try to fix it in a way that doesn't break other files.

[402Martin]

Sorry @iulica, just realized I had 2 clones of the repo and runned the tests on the incorrect directory, will work on the fix and reopen once they run correctly. and add some tests for this

Apologise for all the issues