Add CI

.github/workflows/ci.yml

+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: dependencies
+      run: sudo apt-get install libpcaudio-dev libsonic-dev ronn kramdown
+    - name: autoconf
+      run: ./autogen.sh ; chmod -x INSTALL m4/*.m4
+    - name: configure
+      run: ./configure
+    - name: make
+      run: make
+    - name: make check
+      run: make check