Functions naming and doc comments improvements

[ilitteri]

Context: P256VERIFY.yul

Description:

Descriptions of the functions returning constants defining the curve and the field are unclear.

Recommendation:

We recommend updating the wording of the description of a couple of functions. We suggest to use Recommended Elliptic Curve Domain Parameters as a reference.

1. P256VERIFY.yul#L12 P() is a prime number which defines the field which is a domain of the curve parameters.
2. P256VERIFY.yul#L19. N() is the order of generator G.

[ilitteri]

Resolved in #200