removes uneeded console.log
big one. adds spawning workers. moves tweet logic to separate module.

app.js spawns pool of workers to poll SQS.
TODO: send tweets to SQS for sentiment analysis.

moves all of the tweet logic into tweets.js module.
tweets are saved to dynamo in batches of 25.
TODO handle exceeding dynamo write-throughput
removes keys.sample.js. no longer needed
grind into coffee