Adds basic support for the Swift programming language

Text only lexer for now until Pygments catches up

samples/Swift/section-57.swift

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+class EquilateralTriangle: NamedShape {
+    var sideLength: Double = 0.0
+
+    init(sideLength: Double, name: String) {
+        self.sideLength = sideLength
+        super.init(name: name)
+        numberOfSides = 3
+    }
+
+    var perimeter: Double {
+        get {
+             return 3.0 * sideLength
+        }
+        set {
+            sideLength = newValue / 3.0
+        }
+    }
+
+    override func simpleDescription() -> String {
+        return "An equilateral triagle with sides of length \(sideLength)."
+    }
+}
+var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
+triangle.perimeter
+triangle.perimeter = 9.9
+triangle.sideLength