Use Vite for demo page

Author: kazk

.github/workflows/publish-demo.yml

@@ -0,0 +1,20 @@
+name: Publish Demo
+on:
+  push:
+    branches:
+      - main
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
+        with:
+          node-version: '16'
+          cache: 'npm'
+      - run: npm ci
+      - run: npm run build
+      - uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./dist

.gitignore

@@ -1,3 +1,4 @@
 .DS_Store
 *.log
 node_modules/
+dist/

.node-version

@@ -0,0 +1 @@
+v16.13.2

README.md

@@ -1,3 +1,9 @@
 # codemirror-lambda-calculus
 
 Lambda Calculus mode for CodeMirror.
+
+- `defineMode(CodeMirror)`: Define `lambdacalc` mode and MIME `text/x-lambdacalc`
+
+## Development
+
+Run `npm run dev` to start a local dev server.