Converts a file extension to the related MIME value (.pdf to application/pdf) and converts a MIME value to the default extension (text/html to .htm). Useful for webservers / browsers, as it uses the windows MIME values in the registry, rather than programs having their own copy of each value.
Inputs
Either the extension of the file, or the MIME value of the file.
Returns
Either a MIME type or extension - depending on the information supplied.