Aqtinstall

Fixed
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* Fixed failure when installing Qt5.7 which archives use 7zip(LZMA1+BCJ), that is supported
by py7zr v0.9 and later.(149,150)

Added
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* Add Qt6 as a known version. (144)


Fixed
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* Support package directory 'qt6_*' as well as 'qt5_*' (145)

Changed
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* Do not raise exception when specified combination is not found on downloaded meta data.
* Update document for developers.

Added
--------

* New subcommand doc/src/example to install each components.(137, 138)
* Doc: Add CLI example for tools, doc, examples and src.

Changed
----------

* Refactoring to reduce code duplication in archives.py
* Explicitly call QtInstall.finalize() only when Qt library installation.

Fixed
------

* Show help when launched without any argument (136)