[feature] support OpenSSH key format

[koba-e964]

Supporting OpenSSH keys can be a way forward. Examples of keys: https://github.com/koba-e964/clavem/tree/master/data/openssh

I think I can implement it given some time.

[wader]

Hey, looks like the format partially uses ASN1 and fq has a ASN1 BER decoder so that might be useful. I would probably just get started somewhere and see how it goes. I'm happy to help out if you get stuck.