feat: replace IO class with System class and remove separate IO module

- Delete wren_io.c, wren_io.h, and io.wren source files
- Remove multi-arity print overloads and IO.read/IO.time methods
- Add System class with print, printAll, write, writeAll methods to core.wren
- Update all documentation examples and README to use System.print instead of IO.print

test/language/static_field/closure.wren

@@ -11,6 +11,6 @@ class Foo {
 }
 
 Foo.initialize
-IO.print(Foo.closeOverGet.call()) // expect: Foo field
+System.print(Foo.closeOverGet.call()) // expect: Foo field
 Foo.closeOverSet.call()
-IO.print(Foo.closeOverGet.call()) // expect: new value
+System.print(Foo.closeOverGet.call()) // expect: new value

test/language/static_field/default_to_null.wren

@@ -1,5 +1,5 @@
 class Foo {
-  static write { IO.print(__field) }
+  static write { System.print(__field) }
 }
 
 Foo.write // expect: null

test/language/static_field/in_instance_method.wren

@@ -10,11 +10,11 @@ class Foo {
   }
 
   write() {
-    IO.print(__a)
-    IO.print(__b)
-    IO.print(__c)
-    IO.print(__d)
-    IO.print(__e)
+    System.print(__a)
+    System.print(__b)
+    System.print(__c)
+    System.print(__d)
+    System.print(__e)
   }
 }
 

test/language/static_field/multiple.wren

@@ -8,11 +8,11 @@ class Foo {
   }
 
   static write {
-    IO.print(__a)
-    IO.print(__b)
-    IO.print(__c)
-    IO.print(__d)
-    IO.print(__e)
+    System.print(__a)
+    System.print(__b)
+    System.print(__c)
+    System.print(__d)
+    System.print(__e)
   }
 }
 

test/language/static_field/nested_class.wren

@@ -3,36 +3,36 @@ class Outer {
 
   static staticMethod {
     __field = "outer"
-    IO.print(__field) // expect: outer
+    System.print(__field) // expect: outer
 
     class Inner {
       construct new() {}
 
       static staticMethod {
         __field = "inner"
-        IO.print(__field) // expect: inner
+        System.print(__field) // expect: inner
       }
     }
 
     Inner.staticMethod
-    IO.print(__field) // expect: outer
+    System.print(__field) // expect: outer
   }
 
   instanceMethod {
     __field = "outer"
-    IO.print(__field) // expect: outer
+    System.print(__field) // expect: outer
 
     class Inner {
       construct new() {}
 
       instanceMethod {
         __field = "inner"
-        IO.print(__field) // expect: inner
+        System.print(__field) // expect: inner
       }
     }
 
     Inner.new().instanceMethod
-    IO.print(__field) // expect: outer
+    System.print(__field) // expect: outer
   }
 }
 

test/language/static_field/use_before_set.wren

@@ -1,5 +1,5 @@
 class Foo {
-  static write { IO.print(__field) } // Compile a use of the field...
+  static write { System.print(__field) } // Compile a use of the field...
   static init { __field = "value" }  // ...before an assignment to it.
 }