Relax regex conditions to capture more characters in filenames

[igitur]

Hi

I happened to bump into more cases where the regexes were failing. So I made some changes:

• Accommodate all Excel file extensions: .xls, .xlsx, .xlsm, .xlsb
• Accept any character except ' in book and sheet names.
• Other refactoring, like the extensions variable.

[eehlers]

Merged to branch v1.22.x