refactor(async): providers refactor

* refactor(async): providers refactor from #82

* test: providers dedupes redundant providers

* added feedback from PR review

* aegir - increase bundle size to 222kB

.aegir.js

@@ -1,4 +1,4 @@
 module.exports = {
-    bundlesize: { maxSize: '197kB' }
+    bundlesize: { maxSize: '222kB' }
 }
 

package.json

@@ -54,6 +54,7 @@
     "merge-options": "^1.0.1",
     "multihashes": "~0.4.14",
     "multihashing-async": "~0.5.2",
+    "p-queue": "^5.0.0",
     "peer-id": "~0.12.2",
     "peer-info": "~0.15.1",
     "priorityqueue": "~0.2.1",
@@ -62,6 +63,7 @@
     "protons": "^1.0.1",
     "pull-length-prefixed": "^1.3.2",
     "pull-stream": "^3.6.9",
+    "pull-stream-to-async-iterator": "^1.0.1",
     "varint": "^5.0.0",
     "xor-distance": "^2.0.0"
   },

src/index.js

@@ -537,7 +537,8 @@ class KadDHT extends EventEmitter {
 
     const errors = []
     waterfall([
-      (cb) => this.providers.addProvider(key, this.peerInfo.id, cb),
+      // TODO: refactor this in method in async and remove this wrapper
+      (cb) => promiseToCallback(this.providers.addProvider(key, this.peerInfo.id))(err => cb(err)),
       (cb) => this.getClosestPeers(key.buffer, cb),
       (peers, cb) => {
         const msg = new Message(Message.TYPES.ADD_PROVIDER, key.buffer, 0)

src/private.js

@@ -511,7 +511,7 @@ module.exports = (dht) => ({
   async _findNProvidersAsync (key, providerTimeout, n) {
     const out = new LimitedPeerList(n)
 
-    const provs = await promisify(cb => dht.providers.getProviders(key, cb))()
+    const provs = await dht.providers.getProviders(key)
 
     provs.forEach((id) => {
       let info