Turn layout constraints created with anchors into the old API so it works before iOS 9

anchor-conversion.swift

// TODO: greater than, less than, multipliers, constants

import Foundation

let input = "[container.trailingAnchor constraintEqualToAnchor:childView.trailingAnchor]"

func attribute(fromAnchor anchor: String) -> String {
    if let range = anchor.rangeOfString("Anchor") {
        var s = anchor.substringToIndex(range.startIndex)
        let firstChar = s.removeAtIndex(s.startIndex)
        return "NSLayoutAttribute" + String(firstChar).uppercaseString + s
    }
    return "BAD"
}

let separators = NSCharacterSet(charactersInString: "[]. :")
let components = input.componentsSeparatedByCharactersInSet(separators).filter { $0 != "" }

components

let output = "[NSLayoutConstraint constraintWithItem:\(components[0]) attribute:\(attribute(fromAnchor: components[1])) relatedBy:NSLayoutRelationEqual toItem:\(components[3]) attribute:\(attribute(fromAnchor: components[4])) multiplier:1 constant:0]"