Revert "Revert "add swift version control and adapted to older versio…

…ns.""

This reverts commit 6c0edd6.

Sources/Kanna/CSS.swift

@@ -155,7 +155,11 @@ private let matchSubContains  = firstMatch("contains\\([\"\'](.*?)[\"\']\\)")
 
 private func substringWithRangeAtIndex(_ result: AKTextCheckingResult, str: String, at: Int) -> String {
     if result.numberOfRanges > at {
+        #if swift(>=4.0)
+        let range = result.range(at: at)
+        #else
         let range = result.rangeAt(at)
+        #endif
         if range.length > 0 {
             let startIndex = str.index(str.startIndex, offsetBy: range.location)
             let endIndex = str.index(startIndex, offsetBy: range.length)
@@ -321,7 +325,11 @@ private func getAttrNot(_ str: inout String, skip: Bool = true) -> String? {
         if let attr = getAttribute(&one, skip: false) {
             return attr
         } else if let sub = matchElement(one) {
+            #if swift(>=4.0)
+            let range = sub.range(at: 1)
+            #else
             let range = sub.rangeAt(1)
+            #endif
             let startIndex = one.index(one.startIndex, offsetBy: range.location)
             let endIndex   = one.index(startIndex, offsetBy: range.length)