Switch to Qt6 (#69)

* Now library supports only Qt6. We've updated interface of the main classes in compliance with Qt6:
  * QList<QString> instead of QStringList
  * QStringConverter::Encoding instead of QTextCodec
  * qsizetype instead of int
* Simplification - no more PIMPL classes
* Switch to C++11/14/17
* Minor code style changes
* Move all CI jobs to Appveyor

New contributors: Bogdan Cristea (https://github.com/cristeab), Markus Krause (https://github.com/markusdd)

CMakeLists.txt

@@ -1,23 +1,14 @@
 cmake_minimum_required (VERSION 3.0)
 
-project (qtcsv VERSION 1.6.0 LANGUAGES CXX)
+project (qtcsv VERSION 1.7.0 LANGUAGES CXX)
 
 # set options
 option(STATIC_LIB "build as static lib if ON, otherwise build shared lib" OFF)
-option(USE_QT4 "builds against Qt4 if ON, otherwise builds against Qt5" OFF)
 option(BUILD_TESTS "build tests" ON)
 
 # find qt package
-if(USE_QT4)
-    find_package(Qt4 REQUIRED)
-    set(QT_CORE_TARGET Qt4::QtCore)
-else()
-    # if cmake failed to find Qt5Core configuration file, set path manually:
-    #list(APPEND CMAKE_PREFIX_PATH "/path/to/Qt/lib/cmake/Qt5Core/")
-
-    find_package(Qt5Core REQUIRED)
-    set(QT_CORE_TARGET Qt5::Core)
-endif(USE_QT4)
+find_package(Qt6 COMPONENTS Core REQUIRED)
+set(QT_CORE_TARGET Qt6::Core)
 
 # instruct CMake to run moc automatically when needed.
 set(CMAKE_AUTOMOC ON)