AppVeyor: larger updates in build configuration and documentation
diff --git a/appveyor.yml b/appveyor.yml
index d19eeba..7a0a3d9 100755
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -28,15 +28,13 @@
     - master
     - /^(release/)?\d+\.\d+\.\d+$/
 
-os:
-  - Visual Studio 2017
-
 matrix:
   fast_finish: true
 
 environment:
   matrix:
    - PROFILE: MSVC2017
+     APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
      PLATFORM: x64
      CONFIGURATION: Release
      BUILD_SHARED_LIBS: ON
@@ -47,6 +45,7 @@
      ZLIB_VERSION: 1.2.11
 
    - PROFILE: MSVC2015
+     APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
      PLATFORM: x86
      CONFIGURATION: Debug
      BUILD_SHARED_LIBS: OFF
@@ -55,7 +54,6 @@
      PYTHON_VERSION: 3.5
      QT_VERSION: 5.8
      ZLIB_VERSION: 1.2.8
-     APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
 
    - PROFILE: MINGW
      # Currently the the latest MSYS2 is in the following image:
@@ -64,10 +62,10 @@
      CONFIGURATION: RelWithDebInfo
      DISABLED_TESTS: (StalenessCheckTest)
 
-   - PROFILE: CYGWIN
-     PLATFORM: x64
-     CONFIGURATION: RelWithDebInfo
-     DISABLED_TESTS: (ZlibTest|OpenSSLManualInitTest|TNonblockingServerTest)
+   #- PROFILE: CYGWIN
+   #  PLATFORM: x64
+   #  CONFIGURATION: RelWithDebInfo
+   #  DISABLED_TESTS: (ZlibTest|OpenSSLManualInitTest|TNonblockingServerTest)
 
 install:
   - cd %APPVEYOR_BUILD_FOLDER%