Support vendor defined error codes

[hug-dev]

Vendor defined error codes are still not handled nicely. As a vendor, you probably do something like this:

#define CKR_MY_ERROR_A (CKR_VENDOR_DEFINED+1)
#define CKR_MY_ERROR_B (CKR_VENDOR_DEFINED+2)
#define CKR_MY_ERROR_C (CKR_VENDOR_DEFINED+3)

In cryptoki 0.10.0, these will be mapped to RvError::GeneralError. Therefore, as a cryptoki user I cannot distinguish between the vendor-defined errors.

From Section 3.6 of the standard v3.1:

Return values CKR_VENDOR_DEFINED and above are permanently reserved for token vendors.

So it should be safe to map these to something like RvError::VendorDefined(code).

Originally posted by @thgoebel in #54

A similar approach than #246 should probably be acceptable there!