"IO" -> "System".

Get rid of the separate opt-in IO class and replace it with a core
System class.

- Remove wren_io.c, wren_io.h, and io.wren.
- Remove the flags that disable it.
- Remove the overloads for print() with different arity. (It was an
  experiment, but I don't think it's that useful.)
- Remove IO.read(). That will reappear using libuv in the CLI at some
  point.
- Remove IO.time. Doesn't seem to have been used.
- Update all of the tests, docs, etc.

I'm sorry for all the breakage this causes, but I think "System" is a
better name for this class (it makes it natural to add things like
"System.gc()") and frees up "IO" for referring to the CLI's IO module.

test/benchmark/binary_trees.wren

@@ -24,10 +24,10 @@ var minDepth = 4
 var maxDepth = 12
 var stretchDepth = maxDepth + 1
 
-var start = IO.clock
+var start = System.clock
 
-IO.print("stretch tree of depth ", stretchDepth, " check: ",
-    Tree.new(0, stretchDepth).check)
+System.print("stretch tree of depth " + stretchDepth.toString + " check: " +
+    Tree.new(0, stretchDepth).check.toString)
 
 var longLivedTree = Tree.new(0, maxDepth)
 
@@ -44,10 +44,12 @@ while (depth < stretchDepth) {
     check = check + Tree.new(i, depth).check + Tree.new(-i, depth).check
   }
 
-  IO.print((iterations * 2), " trees of depth ", depth, " check: ", check)
+  System.print((iterations * 2).toString + " trees of depth " +
+      depth.toString + " check: " + check.toString)
   iterations = iterations / 4
   depth = depth + 2
 }
 
-IO.print("long lived tree of depth ", maxDepth, " check: ", longLivedTree.check)
-IO.print("elapsed: ", (IO.clock - start))
+System.print("long lived tree of depth " + maxDepth.toString + " check: " +
+    longLivedTree.check.toString)
+System.print("elapsed: " + (System.clock - start).toString)

test/benchmark/delta_blue.wren

@@ -92,7 +92,7 @@ class Constraint {
     chooseMethod(mark)
     if (!isSatisfied) {
       if (_strength == REQUIRED) {
-        IO.print("Could not satisfy a required constraint!")
+        System.print("Could not satisfy a required constraint!")
       }
       return null
     }
@@ -102,7 +102,7 @@ class Constraint {
     var overridden = out.determinedBy
     if (overridden != null) overridden.markUnsatisfied
     out.determinedBy = this
-    if (!ThePlanner.addPropagate(this, mark)) IO.print("Cycle encountered")
+    if (!ThePlanner.addPropagate(this, mark)) System.print("Cycle encountered")
     out.mark = mark
     return overridden
   }
@@ -669,31 +669,31 @@ var projectionTest = Fn.new {|n|
 
   change.call(src, 17)
   total = total + dst.value
-  if (dst.value != 1170) IO.print("Projection 1 failed")
+  if (dst.value != 1170) System.print("Projection 1 failed")
 
   change.call(dst, 1050)
 
   total = total + src.value
-  if (src.value != 5) IO.print("Projection 2 failed")
+  if (src.value != 5) System.print("Projection 2 failed")
 
   change.call(scale, 5)
   for (i in 0...n - 1) {
     total = total + dests[i].value
-    if (dests[i].value != i * 5 + 1000) IO.print("Projection 3 failed")
+    if (dests[i].value != i * 5 + 1000) System.print("Projection 3 failed")
   }
 
   change.call(offset, 2000)
   for (i in 0...n - 1) {
     total = total + dests[i].value
-    if (dests[i].value != i * 5 + 2000) IO.print("Projection 4 failed")
+    if (dests[i].value != i * 5 + 2000) System.print("Projection 4 failed")
   }
 }
 
-var start = IO.clock
+var start = System.clock
 for (i in 0...40) {
   chainTest.call(100)
   projectionTest.call(100)
 }
 
-IO.print(total)
-IO.print("elapsed: ", IO.clock - start)
+System.print(total)
+System.print("elapsed: " + (System.clock - start).toString)

test/benchmark/fib.wren

@@ -5,8 +5,8 @@ class Fib {
   }
 }
 
-var start = IO.clock
+var start = System.clock
 for (i in 1..5) {
-  IO.print(Fib.get(28))
+  System.print(Fib.get(28))
 }
-IO.print("elapsed: ", IO.clock - start)
+System.print("elapsed: " + (System.clock - start).toString)

test/benchmark/fibers.wren

@@ -2,7 +2,7 @@
 var fibers = []
 var sum = 0
 
-var start = IO.clock
+var start = System.clock
 
 for (i in 0...100000) {
   fibers.add(Fiber.new {
@@ -12,5 +12,5 @@ for (i in 0...100000) {
 }
 
 fibers[0].call()
-IO.print(sum)
-IO.print("elapsed: ", IO.clock - start)
+System.print(sum)
+System.print("elapsed: " + (System.clock - start).toString)

test/benchmark/for.wren

@@ -1,10 +1,10 @@
 var list = []
 
-var start = IO.clock
+var start = System.clock
 for (i in 0...1000000) list.add(i)
 
 var sum = 0
 for (i in list) sum = sum + i
 
-IO.print(sum)
-IO.print("elapsed: ", IO.clock - start)
+System.print(sum)
+System.print("elapsed: " + (System.clock - start).toString)

test/benchmark/map_numeric.wren

@@ -1,4 +1,4 @@
-var start = IO.clock
+var start = System.clock
 
 var map = {}
 
@@ -10,10 +10,10 @@ var sum = 0
 for (i in 1..1000000) {
   sum = sum + map[i]
 }
-IO.print(sum)
+System.print(sum)
 
 for (i in 1..1000000) {
   map.remove(i)
 }
 
-IO.print("elapsed: ", IO.clock - start)
+System.print("elapsed: " + (System.clock - start).toString)

test/benchmark/map_string.wren

@@ -77,7 +77,7 @@ for (animal in animals) {
   }
 }
 
-var start = IO.clock
+var start = System.clock
 
 var map = {}
 
@@ -96,5 +96,5 @@ for (key in keys) {
   map.remove(key)
 }
 
-IO.print(sum)
-IO.print("elapsed: ", IO.clock - start)
+System.print(sum)
+System.print("elapsed: " + (System.clock - start).toString)

test/benchmark/method_call.wren

@@ -28,7 +28,7 @@ class NthToggle is Toggle {
   }
 }
 
-var start = IO.clock
+var start = System.clock
 var n = 100000
 var val = true
 var toggle = Toggle.new(val)
@@ -46,7 +46,7 @@ for (i in 0...n) {
   val = toggle.activate.value
 }
 
-IO.print(toggle.value)
+System.print(toggle.value)
 
 val = true
 var ntoggle = NthToggle.new(val, 3)
@@ -64,5 +64,5 @@ for (i in 0...n) {
   val = ntoggle.activate.value
 }
 
-IO.print(ntoggle.value)
-IO.print("elapsed: ", IO.clock - start)
+System.print(ntoggle.value)
+System.print("elapsed: " + (System.clock - start).toString)

test/benchmark/string_equals.wren

@@ -1,4 +1,4 @@
-var start = IO.clock
+var start = System.clock
 
 var count = 0
 for (i in 1..1000000) {
@@ -20,5 +20,5 @@ for (i in 1..1000000) {
       "another") count = count + 1
 }
 
-IO.print(count)
-IO.print("elapsed: ", IO.clock - start)
+System.print(count)
+System.print("elapsed: " + (System.clock - start).toString)