add egcd and modinv unit tests
add egcd and modinv unit tests

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