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/core/range/iterate.wren

@@ -1,35 +1,35 @@
 // Inclusive.
 var range = 1..3
-IO.print(range.iterate(null)) // expect: 1
-IO.print(range.iterate(1)) // expect: 2
-IO.print(range.iterate(2)) // expect: 3
-IO.print(range.iterate(3)) // expect: false
-IO.print(range.iterate(4)) // expect: false
+System.print(range.iterate(null)) // expect: 1
+System.print(range.iterate(1)) // expect: 2
+System.print(range.iterate(2)) // expect: 3
+System.print(range.iterate(3)) // expect: false
+System.print(range.iterate(4)) // expect: false
 
 // Exclusive
 range = 1...3
-IO.print(range.iterate(null)) // expect: 1
-IO.print(range.iterate(1)) // expect: 2
-IO.print(range.iterate(2)) // expect: false
+System.print(range.iterate(null)) // expect: 1
+System.print(range.iterate(1)) // expect: 2
+System.print(range.iterate(2)) // expect: false
 
 // Negative inclusive range.
 range = 3..1
-IO.print(range.iterate(null)) // expect: 3
-IO.print(range.iterate(3)) // expect: 2
-IO.print(range.iterate(2)) // expect: 1
-IO.print(range.iterate(1)) // expect: false
+System.print(range.iterate(null)) // expect: 3
+System.print(range.iterate(3)) // expect: 2
+System.print(range.iterate(2)) // expect: 1
+System.print(range.iterate(1)) // expect: false
 
 // Negative exclusive range.
 range = 3...1
-IO.print(range.iterate(null)) // expect: 3
-IO.print(range.iterate(3)) // expect: 2
-IO.print(range.iterate(2)) // expect: false
+System.print(range.iterate(null)) // expect: 3
+System.print(range.iterate(3)) // expect: 2
+System.print(range.iterate(2)) // expect: false
 
 // Empty inclusive range.
 range = 1..1
-IO.print(range.iterate(null)) // expect: 1
-IO.print(range.iterate(1)) // expect: false
+System.print(range.iterate(null)) // expect: 1
+System.print(range.iterate(1)) // expect: false
 
 // Empty exclusive range.
 range = 1...1
-IO.print(range.iterate(null)) // expect: false
+System.print(range.iterate(null)) // expect: false