Support buffering

[richardszalay]

The current version extends AppenderSkeleton, which synchronously sends events to Sentry. If the Sentry server has any latency, this can cause the application code to block. If we extended BufferingAppenderSkeleton instead, it would append asynchronously and we would inherit any of its buffering options.

I'm happy to do a PR on this, but I'd like your opinion on whether we should add a separate BufferingSentryAppender or just change the existing one to extend BufferingAppenderSkeleton.

[lukehutton]

I don't think this project is under active development, as I read from one of the comments. I'd happily accept your pull request :)

[rogersillito]

Sounds like a worthwhile improvement to me, although hopefully the original authors will get involved (I had a PR accepted a few months back so they may yet return to this). I've also been using my own fork to keep dependencies updated..