Fix html tag check in content

Not sure why tags in the content are not allowed in this method, but the way it checks for them is naff.
* It doesn't take into account any new html5 tags
* It only checks for a possible space after the tag name, not for any other type of whitespace, like:

```html
<a
    href="...">
```

The solution is to simply check for any possible tag using regular expressions. Is a lot faster too than checking for every single tag of that long array separately.

It now checks for occurrences of:
```<[any letter][0 or more letters or numbers]>```
or:
```<[any letter][0 or more letters or numbers][space or other whitespace]```