add missing interface methods on ABCs
add missing interface methods on ABCs

These methods are present in the docs but not the actual interfaces.

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