Partial Reimplementation of libsecp256k1 in EVM

Designed to Work with ETHASM (mine, not the pyton one)

1. Group Double takes 4 uint256 parameters: x, y, z and infinity and output 4 parameters x, y, z, and infinity of the double (X coordinate = x/z^2, Y coordinate = y/z^3).
2. Group Add takes 8 parameters: x1, y1, z1, infinity1, x2, y2, z2, infinity2 and output 4 parameters x, y, z, and infinity of the addition result
3. Scalarmult currently just use double and add method to do scalar multiplication. Inputs are 5 parameters. x, y, z, infinity, and k.
4. Wrapper shows how to interface scalarmult with Solidity source code
5. Field invert takes 1 parameter and output its inverse mod p
6. All calldataload are offset by 4 to be compatible with Solidity ABI