allow double [[link]] style

Sources/Ink/Internal/Link.swift

@@ -1,23 +1,34 @@
 /**
-*  Ink
-*  Copyright (c) John Sundell 2019
-*  MIT license, see LICENSE file for details
-*/
+ *  Ink
+ *  Copyright (c) John Sundell 2019
+ *  MIT license, see LICENSE file for details
+ */
 
 internal struct Link: Fragment {
     var modifierTarget: Modifier.Target { .links }
-
+    
     var target: Target
     var text: FormattedText
-
+    
     static func read(using reader: inout Reader) throws -> Link {
         try reader.read("[")
+        var double=false
+        if reader.currentCharacter == "[" {
+            // double [[link]] style
+            reader.advanceIndex()
+            double=true
+        }
         let text = FormattedText.read(using: &reader, terminators: ["]"])
         try reader.read("]")
-
+        if double{
+            try reader.read("]")
+        }
+
         guard !reader.didReachEnd else { throw Reader.Error() }
-
-        if reader.currentCharacter == "(" {
+        if double{
+            return Link(target: .url(URL("markdown://"+text.plainText())), text: text)
+        }
+        else if reader.currentCharacter == "(" {
             reader.advanceIndex()
             let url = try reader.read(until: ")")
             return Link(target: .url(url), text: text)
@@ -27,14 +38,14 @@ internal struct Link: Fragment {
             return Link(target: .reference(reference), text: text)
         }
     }
-
+    
     func html(usingURLs urls: NamedURLCollection,
               modifiers: ModifierCollection) -> String {
         let url = target.url(from: urls)
         let title = text.html(usingURLs: urls, modifiers: modifiers)
         return "<a href=\"\(url)\">\(title)</a>"
     }
-
+    
     func plainText() -> String {
         text.plainText()
     }

Sources/Ink/Internal/Reader.swift

@@ -19,7 +19,7 @@ extension Reader {
 
     var didReachEnd: Bool { currentIndex == endIndex }
     var previousCharacter: Character? { lookBehindAtPreviousCharacter() }
-    var currentCharacter: Character { string[currentIndex] }
+    var currentCharacter: Character { if currentIndex>=endIndex{return Character.init("ƒ")} else {return string[currentIndex]} }
     var nextCharacter: Character? { lookAheadAtNextCharacter() }
     var endIndex: String.Index { string.endIndex }