Feature proposal: `unwrap_lamports` instruction

[joncinque]

Problem

As outlined clearly in solana-program/token#87, users want to move lamports from a wrapped SOL account into any other account. This avoids needing to create and close wrapped SOL accounts constantly.

Proposed Solution

Do the same thing as solana-program/token#87, and add a new instruction for discriminant 45 which transfers all lamports to some amount of lamports from a wrapped SOL account into any other account.