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 You need picocms/pico-deprecated only if you're using old plugins, and picocms/pico-theme is obsolete when using a 3rd-party theme.
Pico doesn't require the PHP extensions itself, but erusev/parsedown-extra does. The explicit composer.json requirements are necessary until erusev/parsedown-extra#85 gets merged. Both extensions aren't part of Ubuntu's default LAMP setup anymore.
Symfony YAML >= 3.0 requires PHP >= 5.5.9 and we're currently not planning to raise Pico's PHP requirement.
This reverts commit f251bc83ec995d05e0e33140df22a451c0cfe4af.
* [New] Added before_read_file_meta and get_page_data plugin hooks to
customize page meta data
* [Changed] Make get_files() ignore dotfiles
* [Changed] Make get_pages() ignore Emacs and temp files
* [Changed] Use composer version of Markdown
* [Changed] Other small tweaks
* [Fixed] Date warnings and other small bugs
