Event support in dogstatsd

This PR allow to use DogStatsD to send events.

The event syntax is like this:
`_e{title_length,body_length}:title|body|p:priority|k:aggregation_key|t:alert_type|s:source_type_name|d:date_happened|h:hostname|#tag1,tag2`
Some details:
* Only title and body are required, others are optional, order doesn't matter
* title and body length are computed based on the utf-8 length. (it allows to une "|" in the title and the body). 
* New lines are replaced by two caracters "\n". Which mean a "\n" in the body will be rendered as a new line.

Exemple:
`_e{8,21}My title:The world is burning!|h:my_computer|#danger,on_fire`


I need some review about this protocol modification before adding it everywhere (documentation, librairies, dogstatsd client in the agent, ...).

One last thing: for now, events are sent one by one. I have two solutions to fix it:
* Update our API to allow multiple events
* Use the same endpoint as the agent
What's the best?