* plugin loader(feat): support loading plugins from user defined directories
Extra plugin lookup paths can be set in global reader setting via key
`extra_plugin_paths`. Value of the key can either be a string or an array
of strings.
* build(fix): also purge non-exist plugins on build
* plugin: migrate debug plugin to menu sorter
MenuSorter: forgot to add plugin style change
MenuSorter: worked out the final quirks
* Menu always compressed into tables without missing indexes for ipairs compatibility
* Orphans attached
* Separators no longer count as items
