Break the key-value format algorithm into a couple of methods

refs roidrage/lograge#47
Refactor the key-value formatter spec to use shared examples, refs roidrage/lograge#47
Measure ALL THE FLOATS. refs roidrage/lograge#47

Theory is that in most cases floats indicate timings
Use l2met conventions over lograge conventions for controller/action

Compacts controller=x action=y into source=x#y

Refs #47
Use ':' to separate controller from action in `source`

The librato API only allows certain characters to be used in the source,
refs #47
Change forward slashes in l2met sources to dashes, refs #47
Merge pull request #47 from memberful/l2met-formatter

Support l2met formatter