[BUG] Silent errors on New() #89

Is there an existing issue for this?

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Current Behavior

Currently, the New function only returns a non-nil pointer to a SecureCookie even if an error occured, making it impossible to handle failure if a bad hash/block key is passed.

Expected Behavior

There should be a way to know if something went wrong

Possible solutions:

1. Expose the err property of SecureCookie
2. Have New return an error
3. Return a nil pointer if an error occurs

Steps To Reproduce

s := securecookie.New(hashKey, []byte{}) // invalid block key

Anything else?

No response