Generated interface with type params

[Schahen]

Consider following declaration (an excerpt from node/crypto.d.ts):

    namespace generateKeyPair {
        function __promisify__(type: "rsa", options: RSAKeyPairOptions<'pem', 'pem'>): Promise<{ publicKey: string, privateKey: string }>; 
        function __promisify__(type: "rsa", options: RSAKeyPairOptions<'pem', 'der'>): Promise<{ publicKey: string, privateKey: Buffer }>; 
        function __promisify__(type: "rsa", options: RSAKeyPairOptions<'der', 'pem'>): Promise<{ publicKey: Buffer, privateKey: string }>; 
        function __promisify__(type: "rsa", options: RSAKeyPairOptions<'der', 'der'>): Promise<{ publicKey: Buffer, privateKey: Buffer }>; 
        function __promisify__(type: "rsa", options: RSAKeyPairKeyObjectOptions): Promise<KeyPairKeyObjectResult>;

        function __promisify__(type: "dsa", options: DSAKeyPairOptions<'pem', 'pem'>): Promise<{ publicKey: string, privateKey: string }>; 
        function __promisify__(type: "dsa", options: DSAKeyPairOptions<'pem', 'der'>): Promise<{ publicKey: string, privateKey: Buffer }>; 
        function __promisify__(type: "dsa", options: DSAKeyPairOptions<'der', 'pem'>): Promise<{ publicKey: Buffer, privateKey: string }>; 
        function __promisify__(type: "dsa", options: DSAKeyPairOptions<'der', 'der'>): Promise<{ publicKey: Buffer, privateKey: Buffer }>; 
        function __promisify__(type: "dsa", options: DSAKeyPairKeyObjectOptions): Promise<KeyPairKeyObjectResult>;

        function __promisify__(type: "ec", options: ECKeyPairOptions<'pem', 'pem'>): Promise<{ publicKey: string, privateKey: string }>; 
        function __promisify__(type: "ec", options: ECKeyPairOptions<'pem', 'der'>): Promise<{ publicKey: string, privateKey: Buffer }>; 
        function __promisify__(type: "ec", options: ECKeyPairOptions<'der', 'pem'>): Promise<{ publicKey: Buffer, privateKey: string }>; 
        function __promisify__(type: "ec", options: ECKeyPairOptions<'der', 'der'>): Promise<{ publicKey: Buffer, privateKey: Buffer }>; 
        function __promisify__(type: "ec", options: ECKeyPairKeyObjectOptions): Promise<KeyPairKeyObjectResult>;
    }   

As of now we generate four different interfaces for every combination of publicKey and privateKey while actually in given scenario it really makes sense to generate parametrized interface for reusing it in all declarations.