Minimal scope for security audit

[ignopeverell]

This is a first pass at detailing what could encompass a minimum but still reasonable audit scope. This would focus on cryptographic and consensus-critical code.

• Diff between our version of rust-secp256k1 and upstream.
• Diff between our version of libsecp256k1 and upstream.
• The Grin core crate
• The Grin keychain crate
• The Grin chain crate

If it helps I can produce the diffs for the first 2 points and count the LoC, but overall this shouldn't be that much code.

/cc @Catheryne

Edit: since the 2 first items have been reviewed by JP Aumasson, a full audit on them has become far less pressing. The last 3 items remain important however.

[Catheryne]

I'll contact all the audit companies with this reduced scope and get bids.

[lehnberg]

@ignopeverell can you add wallet crate to this? IIRC we said that would also be included.

[lehnberg]

fixed, and audit is underway.