Improved accessibility, 3D Touch support

• Updates touch handling, improving the long-press experience and adding support for 3D Touch.
• Introduces an accessibility delegate, to provide actions for links within the label.
• Adds the ability to get attributes at a point, particularly for use with 3D Touch.
• Updated examples for Xcode 10.2 and Swift 5 (the pod itself did not need updates).
• Fixes long press delegate call not being invoked unless there was a foreground or background highlight state.
• Fixes not handling adjustsFontForContentSizeCategory. Note that you do need to specify a NSFontAttributeName attribute for this to work, even on vanilla UILabel, when you are setting attributedText.
• Now requires iOS 10 or later, specifically for -[UIAccessibilityElement accessibilityFrameInContainerSpace].