CCGOST: implement GOST 34.10-2012 support

Includes and builds upon GOST R 34.11-2012 patch in pull #68 and implements new Russian standard digital signature algorithm. 

New signature algorithms have short names "gost2012-256" and "gost2012-512" for 256 bit and 512 bit versions respectively.

So far no test cases added to the codebase. I note that there are none present for digital signature with ccgost to begin with. I've only tested that we can generate and sign certificates that are then verified OK by CryptoPro CSP4.0.