Aqtinstall

Added
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* CLI: '--archives' option: it takes multiple module names such as qtbase, qtsvg etc.
This is an advanced option to specify subset of target installation.
There is no guarantee it works. It is not recommended if you are unknown what is doing.

Added
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* Support installation of Qt version for msvc2019
* Add knowledge of components combination on 5.14 and 5.15

Changed
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* Show detailed diagnose message when error happend.
* CI test with Qt 5.14.2 and 5.15.0
* CI test with installed mingw tools compiler.
* Depends on py7zr v0.7.0b2 and later.

Fixed
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* Tools: Fix mingw installation failure.
* Fix --outputdir behavior about path separator on windows

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().

User can control concurrency by customizing settings.ini file and give it by environment variable AQT_CONFIG