WIP: Implement Haproxy PROXY protocol v1 and v2

[Frankkkkk]

Hi,
This MR enables the comprehension of the Haproxy Proxy Protocol v1 & v2.

Still missing:

• Tests
• Documentation
• Examples

Please tell me what do you think about it :-)

Cheers,

[stygmate]

@giampaolo You may consider test and merge this pull request. Where in the kubernetes aera and i and many other need proxy protocol for being able to keep real ip in "proxy to kubernetes cluster"'s configuration.

[Frankkkkk]

(We're using this plugin in production for 6+ months without any issue so far)
Sadly I may not be able to add the unit tests but I think that it could be very useful nevertheless !