(CTH-91) Add binary onMessage Handler
(CTH-91) Add binary onMessage Handler

This commit adds a binary onMessage handler function that mimics what
we're doing in the on text handler.

Eventually we will likely switch over to only having a binary handler
but for now I'm leaving both in so that we can bench.

puppetlabs/pcp-broker,puppetlabs/pcp-broker,puppetlabs/pcp-broker