Instead of using `*.config.php` files, use `*.yml` files to configure Pico. YAML is much easier to understand, more user friendly and (at least a bit) more error-tolerant, but still very powerful. Don't break BC by letting `PicoDeprecated` still read `config/config.php`.
Currently Pico::getTwigVariables() always returns the default twig variables and ignores all additions/changes made through the onPageRendering event. The method now returns the "real" variables array used by Twig.
Specifying a custom sort method usually means that all pages are sort by a plugin, so Pico's default alphabetical order is overwritten anyway. Letting Pico sort the pages first and discarding the result is burned CPU time...
As previously announced (see [Upgrade to Pico 1.0 page](http://picocms.org/in-depth/upgrade/)) we'll remove the default plugins `PicoParsePagesContent` and `PicoExcerpt` with the next Pico milestone. Needless to say, that you can still install both plugins without any problem - we'll add them to Pico's official [Plugins collection](http://picocms.org/plugins/) by then. Please note that the disadvantages of these plugins are still critical and we strongly advise to not use them. Please refer to the [Upgrade to Pico 1.0 page](http://picocms.org/in-depth/upgrade/) for details.
Execution order matters: if plugin A depends on plugin B, it usually means that plugin B does stuff which plugin A requires. However, Pico loads plugins in alphabetical order, so events might get fired on plugin A before plugin B.
Hence plugins need to be sorted. Pico sorts plugins using a dependency topology, this means that it moves all plugins, on which a plugin depends, in front of that plugin. The order isn't touched apart from that, so they are still sorted alphabetically, as long as this doesn't interfere with the dependency topology. Circular dependencies are being ignored; their behavior is undefiend. Missing dependencies are being ignored until you try to enable the dependant plugin.
This method bases on [Marc J. Schmidt's Topological Sort library](https://github.com/marcj/topsort.php) in version 1.1.0, licensed under the MIT license. It uses the `ArraySort` implementation ([class `\MJS\TopSort\Implementations\ArraySort`](https://github.com/marcj/topsort.php/blob/1.1.0/src/Implementations/ArraySort.php)).
This method can be used to validate and filter input data and can be called via `Pico::getUrlParameter()` (URL GET parameters) and `Pico::getFormParameter()` (HTTP POST parameters). `Pico::filterVariable()` is basically a wrapper for PHP's `filter_var()` function with various compatibility extensions to allow theme developers to use its functionality in Twig templates. Therefore Pico 1.1 adds the `url_param` (`Pico::getUrlParameter()`) and `form_param` (`Pico::getFormParameter()`) Twig functions.
Resolves#305
