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/inherit_fields.wren

@@ -5,8 +5,8 @@ class Foo {
   }
 
   fooPrint {
-    IO.write(_field1)
-    IO.write(_field2)
+    IO.print(_field1)
+    IO.print(_field2)
   }
 }
 
@@ -17,8 +17,8 @@ class Bar is Foo {
   }
 
   barPrint {
-    IO.write(_field1)
-    IO.write(_field2)
+    IO.print(_field1)
+    IO.print(_field2)
   }
 }