Use double instead of stub and mock
Use a mutex to synchronize access to the aggregator
Merge branch 'master' into develop
Bump to v0.6.3.beta.1 [ci skip]
Fix for accessing connection config in Rails 3.0

Also improves the usage of the gemfiles for specific versions.
Bump to v0.6.3.beta.2 [ci skip]
Add working implementation of tagged requests
Refactor and add specs to transmitter and appsignal
Fix and spec the formatter
Remove logging
Bump queue time back to 60 seconds
Fix formatting
Merge pull request #93 from 80beans/tagged_requests

[REVIEW] Add working implementation of tagged requests
Merge branch 'develop' of github.com:80beans/appsignal into develop
Remove ExceptionNotification class
Bump to v0.6.3.beta.3 [ci skip]
Still load config if duplicate API keys are present
Remove version number from log since it's already logged
Bump to v0.6.3 [ci skip]