Do not use project.url for relative link resolution

IMO distributionManagement.site.url should be used instead. Imagine a multi-module site with a distributionManagement url that points to the local file system. A local deploy will move any child sites to sub-directories of the parent (by default), but if you forget to adjust the project urls for all children, the relative links are all wrong because they are calculated from the project urls. There are numerous examples and JIRAs where people are confused about this. Having to specify a url for each single child project is a duplicate information and is also logically not necessary. Note that the distributionManagement url always exists (otherwise the deploy will fail), while the project url is optional. IMO the project url should not be used for the local site generation at all, it is just a piece of user information.