review for emalloc and efree usage, and add free where necessary
review for emalloc and efree usage, and add free where necessary

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