Upgrade HTML Agility Pack version

[craigfowler]

A number of issues have been found with the HTML Agility Pack (HAP), at least one of which would be fixed by a version upgrade. Also, that library is now under new stewardship and so other improvements might have been made.

A recap on the problems:

Crash when writing Unicode characters

Including characters outside of the ANSI character set, but that are not known to HAP can cause a crash in the HtmlEntity.Entitize method.

I believe this is now fixed in a more recent version of HAP. I originally reproduced the issue with Unicode heavy tick and heavy ballot check characters.

Garbage output when writing structure to a document

Writing structure content to a document which includes semicolons and less than symbols (such as JavaScript with a for loop that includes a less-than) results in unwanted garbage double quotes rendered into the document.

It would seem like this is being interpreted as markup and thus the quotes are being added as attributes.

[craigfowler]

Test cases for both of these should be written.

Additionally, if upgrading HAP does not fix then both then issue #224 becomes somewhat more important.

Also, if the upgrade doesn't fix it then a bug sod be raised with HAP.

[craigfowler]

The first part of this was indeed a HAP problem, but the second was actually a mistake in my usage of it. I was attempting to parse the injected script/styles as HTML data, where I should have added it as CDATA.