Add test file for secp256k1_context_create / destroy / clone
Add test file for secp256k1_context_create / destroy / clone

afk11/secp256k1-php,afk11/secp256k1-php,Bit-Wasp/secp256k1-php,afk11/secp256k1-php,Bit-Wasp/secp256k1-php,Bit-Wasp/secp256k1-php,afk11/secp256k1-php,Bit-Wasp/secp256k1-php,Bit-Wasp/secp256k1-php,afk11/secp256k1-php