Rearchitecture, new components

- 4.0 including a lot of significant changes,
it's time to build a solid load tester.

- We'll also want a replayer to work on plog-upshot, added here.

- As we like a single big distro, squeazing all modules in `plog-distro`.

- As we'll want a unique namespace for the distribution and the config
to be exposed everywhere, moving `reference.conf` to `plog-api`
(which kinda makes sense conceptually) and moving server options
to `plog.server`.

- Removing `failedToSend()` from stats as it's been unused for a while now
that Kafka is "just" a handler.
True beginning of a plog client, tests for tags :)
Merge pull request #68 from airbnb/pierre/gigantic

Rearchitecture, new components