Adds basic support for the Swift programming language

Text only lexer for now until Pygments catches up

samples/Swift/section-37.swift

@@ -0,0 +1,9 @@
+func returnFifteen() -> Int {
+    var y = 10
+    func add() {
+        y += 5
+    }
+    add()
+    return y
+}
+returnFifteen()