Support newer ASN.1 signature encoding formats

[tomato42]

SEC 1 v2.0 specifies ECDSA-Sig-Value structure with 4 values, not two, and one alternative formatting:

• ECDSA-Sig-Value with a or y elements
• ECDSA-Full-R structure

add support for creating those signatures and verifying them (create alternatives for

python-ecdsa/src/ecdsa/util.py

Line 365 in 93b04ba

def sigdecode_der(sig_der, order):

and

python-ecdsa/src/ecdsa/util.py

Line 231 in 93b04ba

def sigencode_der(r, s, order):

that can handle them)