Clean up text handling a bit:

- Rename IO.write -> IO.print.
- Make IO.write not print a newline.
- Support \u Unicode escapes in strings.

test/inheritance/is.wren

@@ -5,12 +5,12 @@ var a = new A
 var b = new B
 var c = new C
 
-IO.write(a is A) // expect: true
-IO.write(a is B) // expect: false
-IO.write(a is C) // expect: false
-IO.write(b is A) // expect: true
-IO.write(b is B) // expect: true
-IO.write(b is C) // expect: false
-IO.write(c is A) // expect: true
-IO.write(c is B) // expect: true
-IO.write(c is C) // expect: true
+IO.print(a is A) // expect: true
+IO.print(a is B) // expect: false
+IO.print(a is C) // expect: false
+IO.print(b is A) // expect: true
+IO.print(b is B) // expect: true
+IO.print(b is C) // expect: false
+IO.print(c is A) // expect: true
+IO.print(c is B) // expect: true
+IO.print(c is C) // expect: true