chore: rename temporary file to final filename after successful write

doc/site/core/io.markdown

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+^title IO Class
+^category core
+
+The IO class can be used to read and write to and from the console.
+
+## Static Methods
+
+### IO.print(obj[, obj2, obj3...])
+
+Prints any number of things to the console and then prints a newline
+character. If you don't pass it a string, it will be converted to a string for
+you. When passed multiple things, Wren outputs one after another.
+
+
+	> IO.print("I like bananas")
+	I like bananas
+	> IO.print("Oranges", 10)
+	Oranges10
+	> 
+
+### IO.write(obj)
+
+Prints a single thing to the console, but does not print a newline character
+afterwards. If you pass it something that isn't a string, it will convert it to
+a string.
+
+	> IO.write(4+5)
+	9>
+
+In the above example, the result of `4+5` is printed, and then the prompt is
+printed on the same line because no newline character was printed afterwards.
+
+### IO.read(prompt)
+
+Reads in and returns a line of text from the console. Takes a single string to
+be used as a prompt. Pass an empty string for no prompt. Note that the returned
+line of text includes the newline character at the end.
+
+	> var name = IO.read("Enter your name: ")
+	Enter your name: John
+	> IO.print("Hello " + name + "!")
+	Hello John
+	!
+	>