Breaking changes:
- 'listening' event no longer emits with `port` param
- `server.port` property removed (instead, use
`server.http.address().port`)
Added features:
- expose http server as `server.http`
- expose udp server as `server.udp`
- client.destroy() - ungracefully leave the swarm
- server: added `filter` option to black/whitelist torrents
Bugfixes:
- client considers udp tracker errors to be warnings
- emit 'start', 'stop', 'update', etc. AFTER response sent
- fix udp error response action and message being `undefined`
Internal:
- remove `portfinder` dep
- add complete test for `filter` functionality
