Wanikani-notifier

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* Fixed python 3.6 no longer supported

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* Fixed issue where hidden items were not filtered out
* Improved performances by caching all subjects

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* Updated pushsafer dependencies

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* Fixed reviews not filtered against current user level

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* Improved notifications by allowing the sending of URLs and icons
* Added min option to available_assignments_now CLI command
* Time for available now is no longer set to beginning of hour

* Caused weird timings for lessons

* Fix stop-if-empty option not correctly handled in all cases

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* Fixed lessons not properly retrieved
* Fixed CLI parameters retrieval for notify