language: add unary plus & minus, post increment & decrement operators, non-newline print builtin. fix block comments (#4)

examples/suffix.pork

@@ -0,0 +1,20 @@
+/* Barber shop sign generator! */
+func generatePole(width, height) {
+  var i = 0
+  while i < height {
+    let index = i++ mod width
+    var j = 0
+    while j < width {
+      if j == index { print("#") } else { print("_") }
+      j++
+    }
+    println()
+  }
+}
+
+export func main() {
+  println("nobody:")
+  println()
+  println("barber pole:")
+  generatePole(6, 18)
+}

examples/unary.pork

@@ -0,0 +1,6 @@
+export func main() {
+  let constant = -42
+  println("constant set by unary minus:     ", constant)
+  println("constant modified by unary minus:", -constant)
+  println("constant modified by unary plus: ", +constant)
+}