Fixed
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* Refactoring redirect helper function to improve connection error checks and error message.(109)
* Detect exception on each download and extraction threads.
* Race condition error happend on py7zr. require py7zr>=0.5.3.(97)
* Work around for http://download.qt.io/ returns wrong metalink xml data.(#105, 106)
Changed
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* Support specifying config with environment variable AQT_CONFIG
* Improve error messages when command argument is wrong.
* Allow path search for 7z (96)
* Simplify multi-threading using concurrent.futures.ThreadPoolExecutor().