Adding support for ECC alt-bn128 curve  #516

Description

This specific curve is very popular with zk-SNARKs. A quick skim through libtomcrypt's sources seems to suggest that adding support for this curve should only be matter of adding the appropriate curve parameters in libtomcrypt/src/pk/ecc/ecc.c. I am not a 100% sure of this, but I will be happy to help.