contains(_:) variant to work with Optional<UnicodeScalar>

CharacterSet+ContainsOptionalUnicodeScalar.swift

// Swift 3 

extension CharacterSet {
    /// Test for membership of a particular `UnicodeScalar?` in the `CharacterSet`.
    /// - important: This `contains(_:)` oveload works with `Optional<UnicodeScalar>`
    ///
    /// Consider the following example:
    /// ````
    /// let flowermoji = "💐"
    /// let ucscalar = UnicodeScalar(flowermoji.utf16.last!)
    /// // ucscalar == nil
    ///
    /// if CharacterSet.whitespaces.contains(ucscalar) {
    ///   print("contatins")
    /// }
    /// else {
    ///   print("does not contain")
    /// }
    /// // does not contain
    /// ````
    /// - returns: `false` when `member==.none`, otherwise it works as an original `contains(_: UnicodeScalar)`
    /// - parameter member: optional unicode scalar which membership should be tested
    public func contains(_ member: UnicodeScalar?) -> Bool {
        guard let unicodeScalar: UnicodeScalar = member else {
            return false
        }
        return self.contains(unicodeScalar)
    }
}