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/list/newlines.wren

@@ -8,7 +8,7 @@ var list = [
 
 ]
 
-IO.write(list[0]) // expect: a
-IO.write(list[1]) // expect: b
-IO.write(list[2]) // expect: c
-IO.write(list[3]) // expect: d
+IO.print(list[0]) // expect: a
+IO.print(list[1]) // expect: b
+IO.print(list[2]) // expect: c
+IO.print(list[3]) // expect: d