add support for http analysis in keymetrics

[jamemackson]

from the keymetrics documentation:

Latency route analysis

With this feature you will be able to know which HTTP routes are slower than others. It handles any routing framework.

Only routes with latency over 200 ms and response codes greater than or equal to 500 are shown here.

Usage instructions

To enable this feature you must init pmx before requiring any http module (before requiring express, hapi or other)

require('pmx').init();

var http = require('http');
[...]