Filter objects into Optionals

Filter.swift

extension Filter {

    /// Allows filtering of non sequence types.
    ///
    ///     let label = UILabel().then {
    ///         $0.textAlignment = .Center
    ///         $0.textColor = UIColor.blackColor()
    ///         $0.text = "Hello, World!"
    ///     }
    public func filter(@noescape condition: Self -> Bool) -> Self? {
        return condition(self) ? self : nil
    }

}

extension NSObject: Filter {}