Breaking: upgrade to abstract-level 2

See `UPGRADING.md` for details.

This also removes the majority of documentation from the README in
favor of just linking to the README of `abstract-level` so that we
don't have to maintain two copies.

Category: change

.github/workflows/test.yml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [12, 14, 16]
+        node: [18, 20, 22]
     name: Node ${{ matrix.node }}
     steps:
       - name: Checkout
@@ -15,14 +15,14 @@ jobs:
         with:
           node-version: ${{ matrix.node }}
       - name: Install
-        run: npm install
+        run: npm install --ignore-scripts
       - name: Install Playwright
-        if: matrix.node == 16
+        if: matrix.node == 22
         run: npx playwright install --with-deps
       - name: Test
         run: npm test
       - name: Test browsers
-        if: matrix.node == 16
+        if: matrix.node == 22
         run: npm run test-browsers-local
       - name: Coverage
         run: npm run coverage