Added support for @throws

It is now possible to expect an error by using the following syntax:

```
// @describe validate-ident()

// @it Validate standard ident
validate-ident('hello') is true
// @throws
```

This test will now fail unless call to validate-ident throws an error.

It is possible to provide a regex to test the error message by using:
```
// @throws /This is my error testing regex/
```

The code is not the cleanest and can certainly be refactored should more annotations be added (eg. @shouldNotThrow), but it does the job.