publisher.go: provide documentation
Merge pull request #8 from canaryio/document-publisher

publisher.go: provide documentation
publisher: fix STDOUT reporting, add tests

I mistakenly thought that the `log` package reported to STDOUT, but it
reports to STDERR.  This moves us to `fmt`.

I also added a test for the `StdoutPublisher`.
Merge pull request #9 from canaryio/improve-publisher

publisher: fix STDOUT reporting, add tests
rename canary.go -> main.go
introduce a minimal canaryd
restructure the Sensor for better composition
enable sensors to be stopped
start getting READMEs in line