Set up publishing of @webref/idl with Lerna

Lerna is a tool for managing monorepos, and while @webref/idl is the
only package here now, the packages/* structure makes sense.

Fixes #63.

.github/workflows/test.yml

@@ -0,0 +1,21 @@
+name: Test
+on:
+  pull_request: {}
+  push:
+    branches:
+    - master
+jobs:
+  test:
+    runs-on: ubuntu-18.04
+    strategy:
+      matrix:
+        node-version: ['10', '12', '14']
+    name: Node.js ${{ matrix.node-version }}
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - run: npm ci
+    - run: npx lerna bootstrap
+    - run: npm test

.gitignore

@@ -1,2 +1,3 @@
 node_modules/
+packages/idl/*.idl
 wpt/

lerna.json

@@ -0,0 +1,6 @@
+{
+  "packages": [
+    "packages/*"
+  ],
+  "version": "0.0.1"
+}