added support for secp256r1 curve and updated tests. modified the tests to accept multiple curves

[salmanbaset]

Added support for secp256r1 curve and updated tests. Modified the tests to accept multiple curves.

[salmanbaset]

created PR #7

[salmanbaset]

I have signed the request multiple times and gotten the confirmation, but the status is still pending...

[CLAassistant]

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