Construct an RSA Key pair from raw private components

[Stupremee]

Problem:

It is not possible to construct an rsa::KeyPair from it's raw private components (d, p, q, etc).
In ring I'm able to use KeyPair::from_components method to create an RSA Key from the raw numbers.

I need this API to parse a JWK into a rsa::KeyPair to sign a JWS.

Solution:

Implement the same API ring has, using a PrivateKeyComponents struct and new function

Workaround:

My current workaround includes constructing the private key in DER format using an ASN1 crate, and then use the KeyPair::from_der function. But this is very expensive compared to just creating the key directly