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/is.wren

@@ -1,32 +1,32 @@
-IO.write(Num is Class) // expect: true
-IO.write(true is Bool) // expect: true
-IO.write((fn 1) is Function) // expect: true
-IO.write(123 is Num) // expect: true
-IO.write(null is Null) // expect: true
-IO.write("s" is String) // expect: true
+IO.print(Num is Class) // expect: true
+IO.print(true is Bool) // expect: true
+IO.print((fn 1) is Function) // expect: true
+IO.print(123 is Num) // expect: true
+IO.print(null is Null) // expect: true
+IO.print("s" is String) // expect: true
 
-IO.write(Num is Bool) // expect: false
-IO.write(null is Class) // expect: false
-IO.write(true is Function) // expect: false
-IO.write((fn 1) is Num) // expect: false
-IO.write("s" is Null) // expect: false
-IO.write(123 is String) // expect: false
+IO.print(Num is Bool) // expect: false
+IO.print(null is Class) // expect: false
+IO.print(true is Function) // expect: false
+IO.print((fn 1) is Num) // expect: false
+IO.print("s" is Null) // expect: false
+IO.print(123 is String) // expect: false
 
 // Everything extends Object.
-IO.write(Num is Object) // expect: true
-IO.write(null is Object) // expect: true
-IO.write(true is Object) // expect: true
-IO.write((fn 1) is Object) // expect: true
-IO.write("s" is Object) // expect: true
-IO.write(123 is Object) // expect: true
+IO.print(Num is Object) // expect: true
+IO.print(null is Object) // expect: true
+IO.print(true is Object) // expect: true
+IO.print((fn 1) is Object) // expect: true
+IO.print("s" is Object) // expect: true
+IO.print(123 is Object) // expect: true
 
 // Classes extend Class.
-IO.write(Num is Class) // expect: true
-IO.write(null is Class) // expect: false
-IO.write(true is Class) // expect: false
-IO.write((fn 1) is Class) // expect: false
-IO.write("s" is Class) // expect: false
-IO.write(123 is Class) // expect: false
+IO.print(Num is Class) // expect: true
+IO.print(null is Class) // expect: false
+IO.print(true is Class) // expect: false
+IO.print((fn 1) is Class) // expect: false
+IO.print("s" is Class) // expect: false
+IO.print(123 is Class) // expect: false
 
 // TODO: Non-class on RHS.
 // TODO: Precedence and associativity.