Issue #119 - Test HTML5, custom-tags: no

# About this case

This test case ensures that Tidy handles autonomous custom tags appropriately for HTML5 documents.

In this case, `custom-tags` is no, and so Tidy should report unknown tags. We will use `force-output` to ensure that a document is generated, and to gather additional warning output.

This is a user-defined tag, and Tidy should provide a warning, but allow it. The warning is issued because although being a user-defined tag, there's nothing in the specification that allows such a tag that we know about. This is a user-defined tag, and Tidy should not provide a warning. Although `custom-tags` is no, it looks like an autonomous custom tag, and the user defined it, and so there's no reason to warn about it. This is an autonomous custom tag, but it's not supported in this test case. It should be rejected and cause an error.