Adjust Slack message format to match HipChat's

Also add some tests for formatting. See #586.
altered mysql code to use `mediumblob` instead of `blob` to avoid 64k limit
Merge pull request #631 from bradrydzewski/master

altered mysql to use `mediumblob` instead of `blob` to avoid 64k limit
excluding of unused transformation to []byte

A Readers are more flexible and result in faster code that uses less memory
Merge pull request #632 from takama/master

excluding of unused transformation to []byte
second excluding of unused transformation

sorry, could not grep it all before
Merge pull request #633 from takama/master

second excluding of unused transformation
Merge pull request #613 from ciarand/master

Adjust Slack message format to match HipChat's