Cookie should use itsdangerous for signing

[davidism]

[sblondon]

If I understand well, you'd like secure_cookie.cookie.SecureCookie() uses itsdangerous.Signer() to serialize and unserialize the data.

The serialization algorithms are different in the two libraries so the current released version will not be compatible with the next version using itsdangerous.Signer(). Do you want to keep backward compatibility?
I think the backward compatibility is not important because the sessions have few days lifetime only but perhaps I miss something?

I'm interested to write a PR.

[davidism]

Could probably add a fallback that tried the old algorithm if itsdangerous couldn't decode it. Issue a deprecation warning when that happens, to be removed in 1.1.

cc @xmo-odoo