This is a BC breaking change!
Manipulating Pico's $plugins array is a really bad idea. We've introduced the Pico::loadPlugin() method to safely load plugins at any time, however, Pico might do unexpected things when loading plugins too late. See the class docs of Pico::loadPlugin() for more details. Nevertheless, this change breaks BC to Pico 1.0. However, I don't know a single plugin that relies on manipulating the $plugins array. If you just want to load a plugin manually, use Pico::loadPlugin() instead.
Add new onPagesDiscovered event passing the unsorted pages array, move the $currentPage, $previousPage and $nextPage arguments from the onPagesLoaded event to the new onCurrentPageDiscovered event, remove the $twig argument from the onPageRendering event and rather trigger the new onTwigRegistered event for this. Also add the new onYamlParserRegistered and onParsedownRegistered events passing the YAML parser resp. the Parsedown instance. Allow plugin's to skip a page by setting the $id argument of the onSinglePageLoading event to NULL.
