Add Github CI test

For a limited set of PWAD demos since we can't test with the commercial
IWADs.

.github/workflows/ci.yml

@@ -0,0 +1,40 @@
+name: Continuous Integration
+
+on:
+  push:
+    branches:
+      - "master"
+    tags:
+      - "*"
+    paths-ignore:
+      - "**.md"
+  pull_request:
+    branches:
+      - "master"
+    paths-ignore:
+      - "**.md"
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: Statcheck test
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install make chocolate-doom python3 python3-yaml
+
+      - name: Override demos list
+        run: |
+          echo demos/pwads/av/fast/af253503.zip/af253503.lmp \
+               demos/pwads/hr/movie/11hr7159.zip/11hr7159.lmp \
+               demos/pwads/mm/movie/30mm8356.zip/30mm8356.lmp \
+               demos/pwads/mm2/max/m2221807.zip/m2221807.lmp \
+               demos/pwads/requiem/movie/6039rq01.zip/6039rq01.lmp \
+             > demos.txt
+
+      - name: Test
+        run: |
+          make check