Add SM2 public key and elliptic curve algorithms

SM2 is a 4-part Chinese national standard for public key algorithms, including digital signatures and elliptic curves. See SM2 Digital Signature Algorithm. We recently received some private emails asking for several Chinese algorithms. The email also pointed out US and some European algorithms have good coverage in the library.

Can I help for sm2 something?

@cjl3230,

I'm weak on adding public key algorithms so I have been dragging my feet about it. I wrote some test code a while back and I have several open questions, like how to make some of parameters available to the signing algorithm. (As it stands the PK_Signer interface does not account for it).

@noloader https://github.com/jntass/TASSL.git maybe help you