Plugin installation

Plugins are installed in a few steps.

1. Ensure that root site directory has a plugins directory, if not create it
2. Create a directory for the plugin to be installed in plugins and copy the plugin files there
3. Enable the plugin in site.conf in the [site] section adding <plugin name> to enabled_plugins setting. The list of plugin names must be separated by commas
4. Optionally add any configuration to site.conf, see plugin documentation
5. Optionally add plugin to any hook_* settings if the order of plugin execution is required for correct operation (if not set Pagegen will execute in alphabetical order)