CertificateFingerprints.from_string() now supports plain SHA1 and

SHA256 strings (without the semicolons used in fingerprints). These will

be converted into the correct format.
The values are also now validated against regexes. This will key off

the pattern and information needed to optionally normalize the string

and then set it, based on the length of the string provided. If there

isn't a suitable match, None will be returned.

Unit tests pass.