Allow specifying a checksum of the bin

[Will O'Beirne]

For security-conscious applications, it'd be nice to be able to add a set of hashes for each src that the library checks to make sure the binaries match.

Not sure if this would make more sense as a 4th and 5th arg src(..., [hash], [hash-method]) or as an entirely new call tacked at the end with a map or array of hashes that correspond to each src.