[Feature] Use a Selector (NIO), rather than a thread per connection

[lmprice]

I would like to see the Connection utilize a Selector and a single thread rather than unique reader threads per connection/socket. This will make the library work a lot better when scaling up the number of Topics/Channels being utilized.

I am willing to make/submit this change as a PR.

[robseed]

We spoke over email. Go for it!