Add events feature

README.md

@@ -284,6 +284,16 @@ await db.put('key', 'value')
 
 </details>
 
+### `events` (boolean or object)
+
+Is db an event emitter, as indicated by a truthy value? And does it support specific events as indicated by nested properties?
+
+```js
+if (db.supports.events && db.supports.events.open) {
+  db.once('open', () => { /* .. */})
+}
+```
+
 ### `streams` (boolean)
 
 Does db have the methods `createReadStream`, `createKeyStream` and `createValueStream`, following the API currently documented in `levelup`?

index.js

@@ -29,8 +29,13 @@ module.exports = function supports (...manifests) {
     promises: manifest.promises || false,
     streams: manifest.streams || false,
     encodings: manifest.encodings || false,
+    events: maybeObject(manifest.events),
 
     // Methods that are not part of abstract-leveldown or levelup
     additionalMethods: Object.assign({}, manifest.additionalMethods)
   })
 }
+
+function maybeObject (value) {
+  return !value ? false : Object.assign({}, value)
+}