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/and.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 non-true argument.
-IO.write(false && 1) // expect: false
-IO.write(true && 1) // expect: 1
-IO.write(1 && 2 && false) // expect: false
+IO.print(false && 1) // expect: false
+IO.print(true && 1) // expect: 1
+IO.print(1 && 2 && false) // expect: false
 
 // Return the last argument if all are true.
-IO.write(1 && true) // expect: true
-IO.write(1 && 2 && 3) // expect: 3
+IO.print(1 && true) // expect: true
+IO.print(1 && 2 && 3) // expect: 3
 
 // Short-circuit at the first false argument.
-IO.write(true) && // expect: true
-    IO.write(false) && // expect: false
-    IO.write(false) // should not print
+IO.print(true) && // expect: true
+    IO.print(false) && // expect: false
+    IO.print(false) // 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: true
-IO.write(null && true) // expect: true
-IO.write("" && true) // expect: true
-IO.write(false && true) // expect: false
+IO.print(0 && true) // expect: true
+IO.print(null && true) // expect: true
+IO.print("" && true) // expect: true
+IO.print(false && true) // expect: false