InventoryHtmlReportRenderer#section and InventoryHtmlReportRenderer#link should be non-private

[Vampire]

The InventoryHtmlReportRenderer is nicely customizable with a subclass, as all kinds of methods are protected and can be overridden to do fine-grained customizing.

But for two reasons said methods should have promoted visibility.

1. In the customizing it might be handy to also use these methods.
2. Even if you to not want to use those methods, you get MissingMethodExceptions when non-overridden methods try to call them, due to the Groovy duck-typing and not using static compilation. At least if you use a static language like Kotlin to override the class. I didn't try whether it would work when using Groovy.