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/or.wren

@@ -1,26 +1,26 @@
 // Note: These tests implicitly depend on ints being truthy.
-//       Also rely on IO.write() returning its argument.
+//       Also rely on IO.print() returning its argument.
 
 // Return the first true argument.
-IO.write(1 || true) // expect: 1
-IO.write(false || 1) // expect: 1
-IO.write(false || false || true) // expect: true
+IO.print(1 || true) // expect: 1
+IO.print(false || 1) // expect: 1
+IO.print(false || false || true) // expect: true
 
 // Return the last argument if all are false.
-IO.write(false || false) // expect: false
-IO.write(false || false || false) // expect: false
+IO.print(false || false) // expect: false
+IO.print(false || false || false) // expect: false
 
 // Short-circuit at the first true argument.
-IO.write(false) || // expect: false
-    IO.write(true) || // expect: true
-    IO.write(true) // should not print
+IO.print(false) || // expect: false
+    IO.print(true) || // expect: true
+    IO.print(true) // should not print
 
 // Swallow a trailing newline.
-IO.write(true ||
+IO.print(true ||
     true) // expect: true
 
 // Only false is falsy.
-IO.write(0 || true) // expect: 0
-IO.write(null || true) // expect: null
-IO.write(("" || true) == "") // expect: true
-IO.write(false || true) // expect: true
+IO.print(0 || true) // expect: 0
+IO.print(null || true) // expect: null
+IO.print(("" || true) == "") // expect: true
+IO.print(false || true) // expect: true