Only check the same url only once #58
Description
On Antora based documentation you have some kind of frame for the generated html documentation.
So within these frame maybe there are existing some kind of static urls maybe to reference the github repository where the documentation comes from.
These urls appears on each generated html side, so each of these urls are check for each page is checked.
For performance reason it would be better to checks each url only one time at all.
Maybe it is possible to introduce some kind of caching mechanism for the BrokenHttpUrlChecker.