Expected attribute on <code>, and column+line information on errors

I added a attribute called `expected` on the `<code>` tag. Use it to express in the examples what value you expect, and if the value is not equal to the returned value, it will raise an error. This is useful for not only validating that the code is parsing, but that it is also parsing correctly. Use it like this 
```
<code expect="true"> true == false </code>
``` 
This would raise an error (except if the langue expects true to be equal to false of course) 

Also i added a carrot to show where on the line the parsing error was (if there was one on the last line). Was unsure where on the line the parser had a problem, and figured the information was in the error message.