Moving docker-client instantiation to BuildCommandSequence

and out of the builder constructor so that the constructor doesn't
return an error.  Didn't feel right.
Using a custom type for reporting log and event messages
Removing Error() from event messages (at least for now)

since we're returning any errors on the error channel
Adding status event reporting
Fixing some broken tests
Making sure all logs have a level

and printing them accordingly in the synchronous runner
Setting the default level for docker build messages to debug

(otherwise, apparently, it defaults to panic)
Always report a level when logging
Merge pull request #16 from sylphon/add-event-messages

Add event messages