Create a giveaway (does not post yet).
/giveaway create <prize> <description> <duration> <currency?> <max-per-user?> <scaling?> <base-cost?> <step-cost?> <exponent?> <winners?>
prize: string, description: string, duration: string, currency?: string, max-per-user?: integer, scaling?: string, base-cost?: integer, step-cost?: integer, exponent?: number, winners?: integer