use GitHub Actions across the board

.github/workflows/ci.yml

@@ -15,9 +15,11 @@ jobs:
         version:
           - '1.3'
           - '1'
+          - 'nightly'
         os:
           - ubuntu-latest
           - macOS-latest
+          - windows-latest
         arch:
           - x64
     steps:
@@ -38,3 +40,7 @@ jobs:
             ${{ runner.os }}-
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: codecov/codecov-action@v1
+        with:
+          file: lcov.info

README.md

@@ -2,9 +2,7 @@
 
 [![DOI](https://zenodo.org/badge/20136006.svg)](https://zenodo.org/badge/latestdoi/20136006)
 [![Build Status](https://github.com/JuliaSmoothOptimizers/LinearOperators.jl/workflows/CI/badge.svg?branch=master)
-[![Build status](https://ci.appveyor.com/api/projects/status/kp1o6ejuu6kgskvp/branch/master?svg=true)](https://ci.appveyor.com/project/dpo/linearoperators-jl/branch/master)
 [![Build Status](https://api.cirrus-ci.com/github/JuliaSmoothOptimizers/LinearOperators.jl.svg)](https://cirrus-ci.com/github/JuliaSmoothOptimizers/LinearOperators.jl)
-[![Coveralls](https://coveralls.io/repos/JuliaSmoothOptimizers/LinearOperators.jl/badge.svg?branch=master&service=github)](https://coveralls.io/github/JuliaSmoothOptimizers/LinearOperators.jl?branch=master)
 [![codecov.io](https://codecov.io/github/JuliaSmoothOptimizers/LinearOperators.jl/coverage.svg?branch=master)](https://codecov.io/github/JuliaSmoothOptimizers/LinearOperators.jl?branch=master)
 [![docs](https://img.shields.io/badge/docs-latest-3f51b5.svg)](https://JuliaSmoothOptimizers.github.io/LinearOperators.jl/latest)