197 i would like to have a wallet capable of signing messages implemented in c

[bartossh]

The signer is capable of signing the message. This includes Signer to:

• Create a sha256 digest of the message.
• Precalcule the required signature length (no need to pass a buffer).
• Sign the digest.
• Return Signature structure (signature buffer, signature length, digest buffer, digest length).
• Offer a free method to clean up allocated memory.

[kmroz]

LGTM... 👍🏻

Had 2 small questions regarding the use of OPENSSL_free()/free().