lib secp256k1.cr v0.1.0

initial release for the secp256k1 crystal library

containing:

• the constants describing the elliptic curve #1
• the four Secp256k1:: key functions for ec_mul, ec_add, ec_double, and ec_mod_inv #1
• utilities to generate private and public keys #1
• tests for the secp256k1 module #1
• a struct for EC_Point #1
• github actions checking format and spec #2
• a meaningful readme #3