Added support for HMAC backend
Added support for HMAC backend

kimvais/cryptography,Hasimir/cryptography,Ayrx/cryptography,sholsapp/cryptography,skeuomorf/cryptography,dstufft/cryptography,kimvais/cryptography,Ayrx/cryptography,Ayrx/cryptography,bwhmather/cryptography,dstufft/cryptography,kimvais/cryptography,Ayrx/cryptography,sholsapp/cryptography,sholsapp/cryptography,dstufft/cryptography,sholsapp/cryptography,dstufft/cryptography,skeuomorf/cryptography,Hasimir/cryptography,bwhmather/cryptography,dstufft/cryptography,Lukasa/cryptography,skeuomorf/cryptography,kimvais/cryptography,bwhmather/cryptography,Hasimir/cryptography,Hasimir/cryptography,bwhmather/cryptography,Lukasa/cryptography,Lukasa/cryptography,skeuomorf/cryptography