adonis-websocket PM2 support

Proposed changes

Extract serializing messages for ClusterHop to serializer and add conditional implementation when process is managed by pm2 so messages can be handled by message bus in PM2 module.

See issue #58 for detailed explanation.

Types of changes

What types of changes does your code introduce?

[x] Bugfix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

[x] I have read the CONTRIBUTING doc
[x] Lint and unit tests pass locally with my changes
[ ] I have added tests that prove my fix is effective or that my feature works.
[ ] I have added necessary documentation (if appropriate)

Further comments

Recieved and sent events need to have type when using PM2. I chose the name adonis:hop. This event type needs to be used when listening and emitting messages on PM2 message bus. I wrote a simple PM2 module, which can be used for broadcasting messages. You can install it as follows:

pm2 install ruby184/pm2-adonis

Also when I was testing if everything is working I found that Channel.clusterBroadcast is calling non exisitng method Channel.broadcast, which was renamed to Channel.broadcastPayload in commit https://github.com/adonisjs/adonis-websocket/commit/5a3464ca2eb4cf20724657745bba1c11e3cf2ebb. So I fixed it in this PR.

There is one more bug according to broadcasting to workers. When you use Socket.emitTo method, event is sent only to given IDs on current worker, but then broacasted and sent to ALL sockets for topic on other workers. I will send another PR to fix this issue.

Jul 20 '18 15:07 Ruby184

Coverage decreased (-0.4%) to 93.333% when pulling bbc4af23ccdeac0a1d1cce55ddd3ba3bc51d128c on Ruby184:pm2-support into 27143fdf833b06d565330b2f83c1ce0c46a11f0d on adonisjs:develop.