Merge pull request #106 from GitAlias/shellcheck

Add ShellCheck and fix many warnings

Author: joelparkerhenderson

CODEOWNERS renamed to .github/CODEOWNERS

@@ -0,0 +1,12 @@
+name: ci
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v3
+      - run: ./shellcheck.sh