Handle unstable net connection ingestion

Nobody has claimed this yet.

### Library version

Version: 2.2.0

### What's happening:

We use `logdna-browser` for a capacitor/ionic app but have noticed that when the net goes offline and a log is sent, fetch throws an error which results in the buffer-manager in this library not to send log batches anymore [as seen here](https://github.com/logdna/logdna-browser/blob/20bce037d0be86fd5c154c74601c2dddf42b36eb/src/buffer-manager.ts#L73).

### What should happen:

This library should handle network disconnects and not shut down, which would be the case for web apps on browser and mobile.
Or at least give a hook to the developer so that they can recover by re-initializing.

### Reproduction steps:

In a react/vue/angular sample app, add this library and some logs and `npm start`. Navigate to the app in the browser and either close the connection through the inspection window or just your net connection. The library stops logging.

Start in src/buffer-manager.ts around line 73, where the issue reports that a failed fetch stops later log batches from being sent. Reproduce the behavior in a React, Vue, or Angular sample app with npm start while disabling the network. Done means logging recovers after the connection returns, or the library exposes a documented recovery hook.

Written by the indexing model from the issue text.