support for semicolon separated csv

https://github.com/simonw/csv-diff/blob/0256e49e050077815119a42acc48272624d74cbe/csv_diff/__init__.py#L13

Can you please add ";" in the list of supported delimiters to support CSV generated in countries that uses the "," as decimal point, like Italy?

the line can be modified in this way:

dialect = csv.Sniffer().sniff(peek, delimiters=",\t;")
