[doc] core libfuncs - elliptic curve related libfuncs

[TAdev0]

trafficstars

Parent Task: #68

This issue includes :

    "ec_neg",
    "ec_point_from_x_nz",
    "ec_point_is_zero",
    "ec_point_try_new_nz",
    "ec_point_unwrap",
    "ec_point_zero",
    "ec_state_add",
    "ec_state_add_mul",
    "ec_state_init",
    "ec_state_try_finalize_nz",

[andresmayorca]

Hey, Can I take this one?

[martinvibes]

let me hop on this @mazurroman

[ScottyDavies]

@TAdev0 can you please assign this issue to me?