Make IO a static class instead of a singleton.

test/assignment/associativity.wren

@@ -4,6 +4,6 @@ var c = "c"
 
 // Assignment is right-associative.
 a = b = c
-io.write(a) // expect: c
-io.write(b) // expect: c
-io.write(c) // expect: c
+IO.write(a) // expect: c
+IO.write(b) // expect: c
+IO.write(c) // expect: c

test/assignment/global.wren

@@ -1,8 +1,8 @@
 var a = "before"
-io.write(a) // expect: before
+IO.write(a) // expect: before
 
 a = "after"
-io.write(a) // expect: after
+IO.write(a) // expect: after
 
-io.write(a = "arg") // expect: arg
-io.write(a) // expect: arg
+IO.write(a = "arg") // expect: arg
+IO.write(a) // expect: arg

test/assignment/local.wren

@@ -1,10 +1,10 @@
 fn {
   var a = "before"
-  io.write(a) // expect: before
+  IO.write(a) // expect: before
 
   a = "after"
-  io.write(a) // expect: after
+  IO.write(a) // expect: after
 
-  io.write(a = "arg") // expect: arg
-  io.write(a) // expect: arg
+  IO.write(a = "arg") // expect: arg
+  IO.write(a) // expect: arg
 }.call

test/assignment/syntax.wren

@@ -2,10 +2,10 @@
 var a = "a"
 var b = "b"
 a = b = "chain"
-io.write(a) // expect: chain
-io.write(a) // expect: chain
+IO.write(a) // expect: chain
+IO.write(a) // expect: chain
 
 // Assignment on RHS of variable.
 var c = a = "var"
-io.write(a) // expect: var
-io.write(c) // expect: var
+IO.write(a) // expect: var
+IO.write(c) // expect: var