Import go-http-auth for basic authentication.
Update the Config struct to store HTTP basic auth fields.

A whitespace change was applied to the other fields by gofmt.
Parse the realm, username and password via command line flags.

I set a default realm of "canaryd" for now. Happy to debate.
Warn the user if they fail to set basic auth credentials.

The app is still technically usable, but you can't POST to the /measurements endpoint successfully.
Add an authenticator function to check username and password.

This function will be passed into go-http-auth's BasicAuthenticator.
Initialize an authenticator and wrap the measurements handler.
Merge pull request #33 from anachronistic/anachronistic-http-basic-auth

HTTP Basic Auth for POST /measurements