build: Update Windows to Qt5.15 (#798)

* Update compile howto

- to qt5.15
- minimal install overhead
- sync with vscode and cmake

* Update docs with more input

gh actions windows: Qt5.15 and msvc2019

* fix: Azure build

CompileHowto.md

@@ -78,18 +78,18 @@ brew install doxygen
 We assume a 64bit Windows 7 or higher. Install the following
 - [Git](https://git-scm.com/downloads) (Check: Add to PATH)
 - [Python 3 (Windows x86-64 executable installer)](https://www.python.org/downloads/windows/) (Check: Add to PATH and Debug Symbols)
+  - Open a console window and execute `pip install aqtinstall`.
+  - Now we can download Qt to _C:\Qt_ `mkdir c:\Qt && aqt install -O c:\Qt 5.15.0 windows desktop win64_msvc2019_64`
 - [CMake (Windows win64-x64 Installer)](https://cmake.org/download/) (Check: Add to PATH)
-- [Qt5](https://www.qt.io/download-open-source) (Check: Component install: msvc 2017 64bit). No configuration for PATH is set, we assume the default install path.
-- [Visual Studio 2019 Build Tools](https://go.microsoft.com/fwlink/?linkid=840931)
-  - The Visual Studio 2019 Community Editor is not required but will be installed as part of the compiler and Windows SDK
-  - Select C++ Desktop Development Tools
-  - Now just select `MSVC v142 VS 2019 C++ x64/x86-Buildtools`, `C++-CMake Tools for Windows` and `Windows 10 SDK`. Everything else is not needed.
+- [Visual Studio 2019 Build Tools](https://go.microsoft.com/fwlink/?linkid=840931) ([direct link](https://aka.ms/vs/16/release/vs_buildtools.exe))
+  - Select C++ Buildtools
+  - On the right, just select `MSVC v142 VS 2019 C++ x64/x86-Buildtools` and latest `Windows 10 SDK`. Everything else is not needed.
 
 # Compiling and installing Hyperion
 
 ### The general quick way (without big comments)
 
-complete automated process:
+complete automated process for Mac/Linux:
 ```bash
 wget -qO- https://raw.githubusercontent.com/hyperion-project/hyperion.ng/master/bin/compile.sh | sh
 ```
@@ -161,7 +161,10 @@ cmake -DPLATFORM=osx -DCMAKE_BUILD_TYPE=Release ..
 To generate files on Windows (Release+Debug capable):
 
 Platform should be auto detected and refer to windows, you can also force windows:
-```
+
+```sh
+# You might need to setup MSVC env first
+call "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Auxiliary\Build\vcvars64.bat"
 cmake -DPLATFORM=windows -G "Windows 16 2019" ..
 ```
 
@@ -181,6 +184,7 @@ On Windows run
 ```bash
 cmake --build . --config Release -- -maxcpucount
 ```
+Maintainer: To build installer, install [NSIS](https://nsis.sourceforge.io/Main_Page) and set env `VCINSTALLDIR="C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC"`
 
 ### Install hyperion into your system