Datadog Output and Regex URL Filter

[Osterjour]

I added a Datadog output which is nearly the same as StatsD but with some nice additional features and a new filter which is the regex filter with the possibility add one or more fields for additional parsing (GET params).

[bpaquet]

Before merging, can you ?

• Update the doc to new format
• Provide examples for the url filter : "but has additional parameters to parse the GET params from urls" is not enough for me to understand what the plugin do