A plugin for task timings

I've had this plugin in [another repo](https://github.com/jlafon/ansible-profile) for a while, but I thought you might want to include it in Ansible. 

Installing this plugin will cause task timings to be printed at the end of the playbook, as in this example:
```bash
ansible <args here>
   <normal output here>
   PLAY RECAP ******************************************************************** 
   really slow task  | Download project packages-----------------------------11.61s
   security | Really slow security policies-----------------------------------7.03s
   common-base | Install core system dependencies-----------------------------3.62s
   common | Install pip-------------------------------------------------------3.60s
   common | Install boto------------------------------------------------------3.57s
   nginx | Install nginx------------------------------------------------------3.41s
   serf | Install system dependencies-----------------------------------------3.38s
   duo_security | Install Duo Unix SSH Integration----------------------------3.37s
   loggly | Install TLS version-----------------------------------------------3.36s
```