Update changelog

Julien LepillerTue Jun 09 21:19:20+0200 2020

74a10f5

Update changelog

CHANGELOG.md

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Changes Since 0.2.3
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### Bug Fixes
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* Downloading dictionaries would make some devices almost freeze. Fixed by
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  reducing the rate of UI and notification updates, and by ensuring the file
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  is not kept in memory during its transfer.
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### Features
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* Add a Help screen and two topics: kanji input by component and romaji input.