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/comments/block.wren

@@ -1,5 +1,5 @@
 // In middle of line.
-IO.write/* ... */(/* */"ok"/* */) // expect: ok
+IO.print/* ... */(/* */"ok"/* */) // expect: ok
 
 // Nested.
-IO.write(/* in /* nest */ out */"ok") // expect: ok
+IO.print(/* in /* nest */ out */"ok") // expect: ok

test/comments/block_at_eof.wren

@@ -1,2 +1,2 @@
-IO.write("ok") // expect: ok
+IO.print("ok") // expect: ok
 /* comment */

test/comments/line_at_eof.wren

@@ -1,2 +1,2 @@
-IO.write("ok") // expect: ok
+IO.print("ok") // expect: ok
 // comment

test/comments/unicode.wren

@@ -8,4 +8,4 @@
 
 // TODO: What about combining characters?
 
-IO.write("ok") // expect: ok
+IO.print("ok") // expect: ok

test/comments/unterminated_block.wren

@@ -1,3 +1,3 @@
 // expect error line 3
-IO.write("nope") /*
+IO.print("nope") /*
 oops

test/comments/unterminated_nested_block.wren

@@ -1,4 +1,4 @@
 // expect error line 4
-IO.write("nope") /* /* /*
+IO.print("nope") /* /* /*
 */
 oops