Make File Extension Check Case-Insensitive

[adreichert]

Summary

This PR makes extension check case-insensitive. We've noticed that parsing fails for files with capitalized extension like .PDF. This will permit users to parse files such as *.PDF without having to change the extension to *.pdf.

I confirmed that no elements in SUPPORTED_FILE_TYPES have uppercase letters.

Tested

Attempted to parse file test.PDF. I received an error

Exception: Currently, only the following file types are supported: ['.pdf', '.602', '.abw', '.cgm', '.cwk', '.doc', '.docx', '.docm', '.dot', '.dotm', '.hwp', '.key', '.lwp', '.mw', '.mcw', '.pages', '.pbd', '.ppt', '.pptm', '.pptx', '.pot', '.potm', '.potx', '.rtf', '.sda', '.sdd', '.sdp', '.sdw', '.sgl', '.sti', '.sxi', '.sxw', '.stw', '.sxg', '.txt', '.uof', '.uop', '.uot', '.vor', '.wpd', '.wps', '.xml', '.zabw', '.epub', '.jpg', '.jpeg', '.png', '.gif', '.bmp', '.svg', '.tiff', '.webp', '.htm', '.html', '.xlsx', '.xls', '.xlsm', '.xlsb', '.xlw', '.csv', '.dif', '.sylk', '.slk', '.prn', '.numbers', '.et', '.ods', '.fods', '.uos1', '.uos2', '.dbf', '.wk1', '.wk2', '.wk3', '.wk4', '.wks', '.123', '.wq1', '.wq2', '.wb1', '.wb2', '.wb3', '.qpw', '.xlr', '.eth', '.tsv']
Current file type: .PDF

After making the change I can successfully parse the file.

[jerryjliu]

thanks!