Drop support for appveyor

appveyor.yml

@@ -1,25 +0,0 @@
-environment:
-  matrix:
-    - PYTHON: "C:\\Python35"
-    - PYTHON: "C:\\Python36"
-    - PYTHON: "C:\\Python37"
-    - PYTHON: "C:\\Python38"
-    - PYTHON: "C:\\Python35-x64"
-    - PYTHON: "C:\\Python36-x64"
-    - PYTHON: "C:\\Python37-x64"
-    - PYTHON: "C:\\Python38-x64"
-
-install:
-  - "git submodule update --init --recursive"
-  - "%PYTHON%\\python.exe -m pip install -r requirements-dev.txt"
-
-build: off
-
-test_script:
-  - "build.cmd %PYTHON%\\python.exe setup.py nosetests"
-
-after_test:
-  - "build.cmd %PYTHON%\\python.exe setup.py bdist_wheel"
-
-artifacts:
-  - path: dist\*