Print and log better exceptions when file conversions fail.

[afourney]

Presently, when conversions fail, the converter moves on to the next in the list, and only the final error bubbles up (if no converter worked).

With this fix, all failed conversion attempts are logged and can be accessed in the FileConversionException.attempts attribute. The error message is also more clear. E.g.,

markitdown._exceptions.FileConversionException: File conversion failed after 3 attempts:
 - PptxConverter threw ValueError with message: Testing error handling
 - XlsxConverter threw OSError with message: File contains no valid workbook part
 - DocxConverter threw ValueError with message: Could not find the body element: are you sure this is a docx file?