Adds basic support for the Swift programming language

Text only lexer for now until Pygments catches up

samples/Swift/section-77.swift

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+class SimpleClass: ExampleProtocol {
+     var simpleDescription: String = "A very simple class."
+     var anotherProperty: Int = 69105
+     func adjust() {
+          simpleDescription += "  Now 100% adjusted."
+     }
+}
+var a = SimpleClass()
+a.adjust()
+let aDescription = a.simpleDescription
+
+struct SimpleStructure: ExampleProtocol {
+     var simpleDescription: String = "A simple structure"
+     mutating func adjust() {
+          simpleDescription += " (adjusted)"
+     }
+}
+var b = SimpleStructure()
+b.adjust()
+let bDescription = b.simpleDescription