Initial websocket support

Added godep for gorilla/websocket
Added README snippet
Added handling for creating/tearing down broadcast websockets based on checkID.

Websocket connections can now be made at
<host>:<PORT>/ws/checks/{check_id}/measurements

Logging with remote address
Put websocket handling behind channels

So there can be concurrent access to sending websocket information.
Initially tried a rwMutex but this proved too complicated for minor gain.
Merge pull request #57 from joekarl/ws-support

Initial websocket support
Refactor for test-, mock-ability
Add ability to publish measurements via Redis pub/sub

When REDIS_PUBLISH is set to something other than `no`, publish
measurement with Redis PUBLISH command.  This allows other tools to
consume the measurements in real time.
Add comments
Update test data for correctness

This is closer to what's actually sent by sensord
Update README, make REDIS_PUBLISH flag consistent

REDIS_PUBLISH and LOGSTDERR are both boolean flags; they should be
enabled the same way.