Function decodeEscaped

This function:

1. Keeps regular spaces, only ' ', as they are.
2. Converts \\n \\r and \\t to unescaped versions, \n \r \t.
3. Converts Unicode escape sequences to their control characters.
4. Converts \\' \\and \\\\" to their unescaped versions, ' ".

Unless you're using this in a JSON.parse reviver, you probably want to use decodeEscapedWrapped instead.