Fix JSON pretty printer string escaping

MongoView/JSONPrettyPrinter.swift

@@ -89,7 +89,23 @@ class JSONPrettyPrinter {
     }
     
     private func escape(_ str: String) -> String {
-        return str.replacingOccurrences(of: "\"", with: "\\\"")
+        var str = str
+        var index = str.startIndex
+        while index < str.endIndex {
+            let c = str[index]
+            if c == "\\" || c == "\"" {
+                str.replaceSubrange(index..<str.index(after: index), with: "\\\(c)")
+                index = str.index(after: index)
+            } else if c == "\n" {
+                str.replaceSubrange(index..<str.index(after: index), with: "\\n")
+                index = str.index(after: index)
+            } else if c == "\r" {
+                str.replaceSubrange(index..<str.index(after: index), with: "\\r")
+                index = str.index(after: index)
+            }
+            index = str.index(after: index)
+        }
+        return str
     }
 }