A client for DynamoDB using promises.

Install:

```
npm i dynopromise-client
```

Requires aws-sdk to be installed globally. This is not listed as a hard
dependency, because it is already made available to Lambda functions when
running in the Lambda environment, therefore does not actually need to be
included in your package locally.

Usage:

```
const dynamodb = require('dynopromise-client')
const db = dynamodb({
	accessKeyId: ...,
	secretAccessKey: ...,
	...,
})
db.put({
	TableName: <dynamodb table name>,
	Item: {
		...
	}
})
.then(() => <do something...>)
.catch(err => <handle error...>)
```

Options are passed through to the constructor specificed here:
https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB.html#constructor-property

Promisified methods:
batchGet, batchWrite, createSet, delete, get, put, query, scan, update