[Hash] Allow CRC32 hashing

[paradadf]

Hi again! It would be really great if you could add a flag to allow crc32 hashing, instead of only using sha1. Something like: var crcHash = flag.Bool("crc", false, "Calculate CRC32 checksum instead of SHA1.")

There reason is that some databases have a more complete list of crc32 hashes (i.e. ScreenScraper). To add a rom there, it is mandatory to send crc32 and md5 hashes, but sha1 is only added if you scrape the roms with UXS before AND UXS only calculates/add the sha1 for files lower than 50 Mb (I think).