Adds basic support for the Swift programming language

Text only lexer for now until Pygments catches up

samples/Swift/section-25.swift

@@ -0,0 +1,14 @@
+let interestingNumbers = [
+    "Prime": [2, 3, 5, 7, 11, 13],
+    "Fibonacci": [1, 1, 2, 3, 5, 8],
+    "Square": [1, 4, 9, 16, 25],
+]
+var largest = 0
+for (kind, numbers) in interestingNumbers {
+    for number in numbers {
+        if number > largest {
+            largest = number
+        }
+    }
+}
+largest