* 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
* Start battery stat plugin
* BatteryStat & kobolight
* Several minor improvements
* Remove a useless function
* flush settings
* Some review feedbacks
* Resolve review comments
* Remaining Minutes -> Remaining Hours
* Add dump_file
* typo
* realpath
* realpath on folder
* Remove useless os.time()
* Resolve review comments
* warning
* Add BatteryStat.debugging flag
* treat log as txt
* Minor improvement
* Charging hour should be positive
* Use warn instead of info
* onSuspend in Kobo
* Charging events for kobo and kindle
* More events
* dumpOrLog
* Warnings
* Typo
* More space
* Singleton
* slightly format change
* BatteryStat singleton
* Init
* Remove debugging flag
* sleeping percentage is still negative
* Read settings
* Do not need to change was_suspending and was_charging
* Typo
* Remove debugging flag
* Not charging should happen before suspend
* Resolve review comments
* was_suspend and was_charging should be updated each time in onCallback()
