Add PastelLabel for Issue #11

[cruisediary]

Refactor

• Extract PastelPoint from PastelView

Feature

• Add PastelLabel wrapping UILabel and using mask #11
• Add PastelLabelabel protocol to use PastelLabel like UILabel

public protocol PastelLabelable {
    var text: String? { get set }
    var font: UIFont? { get set }
    var textAlignment: NSTextAlignment { get set }
    var attributedText: NSAttributedString? { get set }
}