General:
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* Supports Qt6 in addition to Qt5
* Minimum Qt version is 5.9
* The qmake buildsystem (via autogen.py) is removed.
* buildsystem: a new 'docs' target is created when CMake -DKDSoap_DOCS=True.
* buildsystem: the API manual is now generated in build/docs vice source/docs.
* buildsystem: added an uninstall target
* buildsystem: generate and install kdsoap-version.h
* The API manual is generated+installed in qch format for Qt assistant.

Client-side:
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* Added options to the KDSoapClient specifying the SOAP action sending method

Server-side:
============

WSDL parser / code generator changes, applying to both client and server side:
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* Fix generated code in case a variable is called "d" or "q" (#118)
* Fix generated code for an enumeration type with a length restriction (#234)
* Avoid potential type collisions in nested complexTypes (#239)