Fix/GH-752 content pages starting with numbers break pdf build

[aprigge]

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For the Title of this pull request, please use the format "Type/Issue-#: Brief description." For Type, the options are Fix, Feature, Docs, or Chore. Issue-# is only needed if this pull request addresses an exisiting issue.

Checklist

Please put an X within the brackets that apply [X].

• [x] I have read the CONTRIBUTING.md file

• [x] I have made my changes in a new branch and not directly in the main branch

• [x] This pull request is ready for final review by the Quire team

Is this pull request related to an open issue? If so, what is the issue number?

752

Please briefly describe the goal of this pull request and how it may impact Quire's functionality.

The PDF would generate and no error would be thrown when a page or directory within content begins with a number.

Please describe the changes you made, and call out any details you think are particularly relevant for the Quire team to note in their review.

Prepend page to selectors derived from files within the content directory.

Does this pull request necessitate changes to Quire's documentation?

n/a

Include screenshots of before/after if applicable.

n/a

Additional Comments

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