Loading veryfying key from pem or der always defaults to sha1 hash function

[bar-bog]

Hi,
first I want to say that your package is great :) Helped me a lot while testing ecdsa on my device.
I have noticed that when you read the verifying key from pem or der format you can't specify hashing function and it defaults to sha1. I think it would be great to have it as a parameter as public key does not specify it.
Maybe I could help you with contribution?

[tomato42]

the default hash function is a public field of the class:
https://github.com/warner/python-ecdsa/blob/0d3d29e9cbc002cae610974b7d934b9accd8134a/src/ecdsa/keys.py#L31

so you can change it after loading it from the file

that being said, both from_string and from_public_point accept the default hash function (the hashfunc parameter), so I don't see why from_pem and from_der couldn't be extended similarly