Convert UTCTime to datetime should care about century

[la10736]

Hi, thanks for the great work!!

I noted that the conversion from utc_datetime() don't try to guess the century. As documented in https://www.obj-sys.com/asn1tutorial/node15.html the year is just 2 chars and asn1c use 19 if the year is greater than 0x35 and 20 otherwise.

I guess that the right behavior of asn1-rs should be the same.

I can file a pull request if you are agree.

[chifflier]

Hi,
Indeed, this should be added to this crate. Currently, callers must take care of changing the offset (for ex in https://github.com/rusticata/x509-parser/blob/master/src/time.rs#L99-L109).
Please submit a PR, I will merge it for the next release (which I plan to do very soon).
Thanks!