Add an example of an async producer

Closes #104
Fixups to ProducerConfig

Closes #87
Closes #99
Merge pull request #106 from Shopify/producer-config-fixes

Fixups to ProducerConfig
Merge pull request #105 from Shopify/async-producer-example

Add an example of an async producer
Add google group link to README
Merge pull request #108 from Shopify/google-group

Add google group link to README
Add go 1.3 to travis configuration
Fix Travis init script
Simple functional test
Merge pull request #107 from Shopify/functional_test

Add functional test
Only run functional tests when Kafka is available. Require that when ENV[CI] is set.
Code review fixes
Merge pull request #110 from Shopify/make_functional_tests_optional

Only run functional tests when Kafka is available
Add producer SendMessages function
Fix thing