Swift 4, Speed x 300, and shouldShowFooter feature!

Summary:

• Library upgraded to Swift 4,
• Speed optimisations to return layout attributes for a given rect by a factor of 300 during scrolling!
• A requested feature to enable the hiding of the footer labels
• Example project updated to reflect the new visual footer hiding configuration.

Technical:

• Example project storyboard removed in favour of a programmatic menu view controller. Makes it easier to demonstrate variations of the DataTableConfiguration object using a GenericDataTableViewController.
• The swift language has been upgraded to swift 4 and runs on xcode 9.
• The DataTableConfiguration object has a new property called shouldShowFooter with a default value of true. This property allows the user to override whether footers should be shown or not.
• Refactors the layoutAttributesForRect method to use a binary search instead of filtering through all cached layouattributes. This sees a speed factory of 300 during scroll.
• Aims to increase the prepare layout method in the SwiftDataTableLayout class by preventing unnecessary delegate calls for column widths.