remove appveyor in favor of github actions

appveyor.yml

@@ -1,28 +0,0 @@
-version: "{build}"
-build: off
-deploy: off
-skip_commits:
-    # add [appveyor skip] as an alias for [skip appveyor] (like [ci skip])
-    message: /\[appveyor skip\]/
-
-environment:
-    matrix:
-        - PYTHON: C:\Python27
-          TOX_ENV: py27-test
-        - PYTHON: C:\Python35
-          TOX_ENV: py35-test
-        - PYTHON: C:\Python36
-          TOX_ENV: py36-test
-        - PYTHON: C:\Python37
-          TOX_ENV: py37-test
-
-# Install Tox for running tests.
-install:
-    - appveyor-retry cinst imagemagick -y
-    # TODO: remove --allow-empty-checksums when unrar offers a proper checksum
-    - appveyor-retry cinst unrar -y --allow-empty-checksums
-    - 'appveyor-retry %PYTHON%/Scripts/pip.exe install "tox<=3.8.1"'
-    - "appveyor-retry %PYTHON%/Scripts/tox.exe -e %TOX_ENV% --notest"
-
-test_script:
-    - "%PYTHON%/Scripts/tox.exe -e %TOX_ENV%"