feat: Async-Iterator interface

This is the next generation of serial port interfaces. Streams are never going away but the async iterator interface is much more flexible. It can be combined with async-iterator tools (such as [streaming-iterables](https://www.npmjs.com/package/streaming-iterables)) to make buffers and parsers, and can even be combined with our existing stream based parsers.

This is very experimental. I’ve tried to bring a lot of these changes in https://github.com/node-serialport/node-serialport/tree/reconbot/typescript2 but I haven’t had time for a full typescript rewrite. So maybe this smaller api change lets us get some of these advantages without having to rewrite everything.

## Todo
- [ ] api feedback
- [ ] build chain to support modern javascript
- [ ] docs for website
- [ ] abstract away get/set/update borrowing from #1679 for local and remote state and parity with web serial
- [ ] tests

## Example Usage
```js
const { open, list } = require('@serialport/async-iterator')
const ports = await list()
const arduinoPort = ports.find(info => (info.manufacture || '').includes('Arduino'))
const port = await open(arduinoPort)

// read bytes until close
for await (const bytes of port) {
  console.log(`read ${bytes.length} bytes`)
}

// read 12 bytes
const { value, end } = await port.next(12)
console.log(`read ${value.length} bytes / port closed: ${end}`)

// write a buffer
await port.write(Buffer.from('hello!'))
```

packages/async-iterator/.npmignore

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+*.test.js
+CHANGELOG.md

packages/async-iterator/LICENSE

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+The MIT License (MIT)
+
+Copyright 2019 Francis Gulotta. All rights reserved.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to
+deal in the Software without restriction, including without limitation the
+rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+sell copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+IN THE SOFTWARE.

packages/async-iterator/README.md

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+# @serialport/AsyncIterator
+
+This is a node SerialPort project! This package does some neat stuff.
+
+- [Guides and API Docs](https://serialport.io/)
+
+This is why you'd use it.
+
+This is how you use it.
+```js
+const asyncIterator = new AsyncIterator()
+
+```

packages/async-iterator/lib/async-iterator.js

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+const DefaultBindings = require('@serialport/bindings')
+const debug = require('debug')('serialport/async-iterator')
+/**
+ * A transform stream that does something pretty cool.
+ * @param {Object} options open options
+ * @example ```
+// To use the `AsyncIterator` interface:
+const { open, list } = require('@serialport/async-iterator')
+const ports = await list()
+const arduinoPort = ports.find(info => (info.manufacture || '').includes('Arduino'))
+const port = await open(arduinoPort)
+
+// read bytes until close
+for await (const bytes of port) {
+  console.log(`read ${bytes.length} bytes`)
+}
+
+// read 12 bytes
+const { value, end } = await port.next(12)
+console.log(`read ${value.length} bytes / port closed: ${end}`)
+
+// write a buffer
+await port.write(Buffer.from('hello!'))
+```
+*/
+
+module.exports.open = async ({ Bindings = DefaultBindings, readSize = 1024, ...openOptions } = {}) => {
+  const port = new Bindings()
+  await port.open(openOptions)
+
+  const next = async (bytesToRead = readSize) => {
+    if (!port.isOpen) {
+      debug('next: port is closed')
+      return { value: undefined, end: true }
+    }
+
+    const readBuffer = Buffer.allocUnsafe(bytesToRead)
+    try {
+      debug(`next: read starting`)
+      const bytesRead = await port.read(readBuffer, 0, bytesToRead)
+      debug(`next: read ${bytesRead} bytes`)
+      const value = readBuffer.slice(0, bytesRead)
+      return { value, end: false }
+    } catch (error) {
+      if (error.canceled) {
+        debug(`next: read canceled`)
+        return { value: undefined, end: true }
+      }
+      debug(`next: read error ${error.message}`)
+      throw error
+    }
+  }
+
+  const asyncIterableIterator = {
+    [Symbol.asyncIterator]: () => asyncIterableIterator,
+    next,
+    write: (data) => port.write(data),
+    close: () => port.close(),
+    update: opt => port.update(opt),
+    set: opt => port.set(opt),
+    get: () => port.get(),
+    flush: () => port.flush(),
+    drain: () => port.drain(),
+  }
+  return asyncIterableIterator
+}
+
+module.exports.DefaultBindings.list

packages/async-iterator/lib/async-iterator.test.js

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+'use strict'
+/* eslint-disable no-new */
+
+const sinon = require('sinon')
+const AsyncIterator = require('./async-iterator')
+
+describe('AsyncIterator', () => {
+  it('constructs', () => {
+    new AsyncIterator()
+  })
+  it('needs more testing')
+})

packages/async-iterator/package.json

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+{
+  "name": "@serialport/async-iterator",
+  "version": "1.0.0",
+  "main": "lib/async-iterator.js",
+  "dependencies": {
+    "debug": "^4.1.1"
+  },
+  "engines": {
+    "node": ">=10.0.0"
+  },
+  "publishConfig": {
+    "access": "public"
+  },
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/node-serialport/node-serialport.git"
+  }
+}