Make IO a static class instead of a singleton.

test/list/insert.wren

@@ -4,41 +4,41 @@
 // Add to empty list.
 var a = []
 a.insert(1, 0)
-io.write(a) // expect: [1]
+IO.write(a) // expect: [1]
 
 // Normal indices.
 var b = [1, 2, 3]
 b.insert(4, 0)
-io.write(b) // expect: [4, 1, 2, 3]
+IO.write(b) // expect: [4, 1, 2, 3]
 
 var c = [1, 2, 3]
 c.insert(4, 1)
-io.write(c) // expect: [1, 4, 2, 3]
+IO.write(c) // expect: [1, 4, 2, 3]
 
 var d = [1, 2, 3]
 d.insert(4, 2)
-io.write(d) // expect: [1, 2, 4, 3]
+IO.write(d) // expect: [1, 2, 4, 3]
 
 var e = [1, 2, 3]
 e.insert(4, 3)
-io.write(e) // expect: [1, 2, 3, 4]
+IO.write(e) // expect: [1, 2, 3, 4]
 
 // Negative indices.
 var f = [1, 2, 3]
 f.insert(4, -4)
-io.write(f) // expect: [4, 1, 2, 3]
+IO.write(f) // expect: [4, 1, 2, 3]
 
 var g = [1, 2, 3]
 g.insert(4, -3)
-io.write(g) // expect: [1, 4, 2, 3]
+IO.write(g) // expect: [1, 4, 2, 3]
 
 var h = [1, 2, 3]
 h.insert(4, -2)
-io.write(h) // expect: [1, 2, 4, 3]
+IO.write(h) // expect: [1, 2, 4, 3]
 
 var i = [1, 2, 3]
 i.insert(4, -1)
-io.write(i) // expect: [1, 2, 3, 4]
+IO.write(i) // expect: [1, 2, 3, 4]
 
 // Returns.inserted value.
-io.write([1, 2].insert(3, 0)) // expect: 3
+IO.write([1, 2].insert(3, 0)) // expect: 3