```
* [New] Improve release & build process and move most build tools to the new
`picocms/ci-tools` repo, allowing them to be used by other projects
* [New] Add page tree; refer to the `Pico::buildPageTree()` method for more
details; also see the `onPageTreeBuilt` event
* [Changed] Update dependencies: Twig 1.35
* [Changed] ! Improve `.htaccess` and deny access to all dot files by default
* [Changed] ! Throw a `RuntimeException` when non-native plugins are loaded,
but Pico's `PicoDeprecated` plugin is not loaded
* [Changed] ! Change `AbstractPicoPlugin::$enabled`'s behavior: setting it to
TRUE now leads to throwing a `RuntimeException` when the plugin's
dependencies aren't fulfilled; use NULL to maintain old behavior
* [Changed] ! Force themes to use `.twig` as file extension for Twig templates
* [Changed] Improve PHP class docs
* [Changed] Various small improvements
```
AbstractPicoPlugin::$enabled now defaults to NULL what leaves the decision whether a plugin should be enabled or disabled by default up to Pico (precisely AbstractPicoPlugin::triggerEvent()). If all dependencies of a plugin are fulfilled, Pico enables the plugin by default. Otherwise the plugin is silently disabled (this was the behavior when AbstractPicoPlugin::$enabled was set to TRUE previously).
If a plugin should never be disabled *silently* (e.g. when dealing with security-relevant stuff like access control, or similar), set AbstractPicoPlugin::$enabled to TRUE. If Pico can't fulfill all the plugin's dependencies, it will throw an RuntimeException.
If a plugin rather does some "crazy stuff" a user should really be aware of before using it, you can set AbstractPicoPlugin::$enabled to FALSE. The user will then have to enable the plugin manually. However, if another plugin depends on this plugin, it might get enabled silently nevertheless.
No matter what, the user can always explicitly enable or disable a plugin in Pico's config.
Deny access to all dot files and dirs by default (except .well-known)
Update nginx rules accordingly and pass denied requests to Pico rather than letting nginx send a 404 response
After resolving a issue, we usually keep it open for about a week to give users some more time for feedback and further questions. This is especially true for issues with the `type: Notice`, `type: Question`, `type: Discussion` and `type: Invalid` labels. After 7 days with no interaction, [Probot](https://probot.github.io/)'s [Stale](https://probot.github.io/apps/stale/) bot (@probot-stale) adds the `info: Stale` label to the issue to ask the participants whether the issue has been resolved. If no more activity occurs, the issue will be automatically closed by @probot-stale 2 days later.
We recommend plugin developers to use templates when serving HTML contents (like the UI of PicoAdmin), however, by supporting multiple file extensions for themes, we make it pretty hard to overwrite a plugin's template with a theme. As always, we preserve BC using PicoDeprecated.
Pico's page tree is a list of all the tree's branches (no matter the depth). Thus, by iterating a array element, you get the nodes of a given branch. All leaf nodes do represent a page, but inner nodes may or may not represent a page (e.g. if there's a `sub/page.md`, but neither a `sub/index.md` nor a `sub.md`, the inner node `sub`, that is the parent of the `sub/page` node, represents no page itself).
A page's file path describes its node's path in the tree (e.g. the page `sub/page.md` is represented by the `sub/page` node, thus a child of the `sub` node and a element of the `sub` branch). However, the index page of a folder (e.g. `sub/index.md`), is *not* a node of the `sub` branch, but rather of the `/` branch. The page's node is not `sub/index`, but `sub`. If two pages are described by the same node (e.g. if both a `sub/index.md` and a `sub.md` exist), the index page takes precedence. Pico's main index page (i.e. `index.md`) is represented by the tree's root node `/` and a special case: it is the only node of the `` (i.e. the empty string) branch.
A node is represented by an array with the keys `id`, `page` and `children`. The `id` key contains a string with the node's name. If the node represents a page, the `page` key is a reference to the page's data array. If the node is a inner node, the `children` key is a reference to its matching branch (i.e. a list of the node's children). The order of a node's children matches the order in Pico's pages array.
If you want to walk the whole page tree, start with the tree's root node at `$pageTree[""]["/"]`. The root node's `children` key is a reference to the `/` branch at `$pageTree["/"]`, that is a list of the root node's direct child nodes and their siblings.
You MUST NOT iterate the page tree itself (i.e. the list of the tree's branches), its order is undefined and the array will be replaced by a non-iterable data structure with Pico 3.0.
Don't lower unregistered meta headers on the first level unsolicited (e.g. `SomeNotRegisteredKey: foobar` in the YAML Frontmatter should result in `['SomeNotRegisteredKey']`, not `['somenotregisteredkey']`). Furthermore, Pico no longer compares registered meta headers in a case-insensitive manner. However, you can now register multiple search strings that are used to find a registered meta header. This is achieved by flipping the meta headers array: Pico 2.0 uses the array key to search for a meta value and the array value to store the found meta value. Previously it was the other way round (what didn't make much sense...).
In the future we'll use picocms/pico-composer to create Pico's release packages (and picocms/pico-composer depends on picocms/pico-deprecated and picocms/pico-theme by default). Installing picocms/pico-deprecated and picocms/pico-theme is no longer required, but rather suggested. You simply don't need them in any case. You need picocms/pico-deprecated only if you're using old plugins, and picocms/pico-theme is obsolete when using a 3rd-party theme.
