Add Nginx support

First draft for doc and the basic conf

Nginx class now extends AbstractCacheProxy #34 - Added purging test for different location setup

Fixing Scrutinizer issue

Update NginxTestCase.php

Refresh method and test

Removed empty line

Few more CS fix

Added nginx as keyword

Added nginx to Travis

Added HTTPS

Typo

Removed empty line

added nginx installation script on travis before_script

Nginx custom build script

Few fix for nginx installation process

Correct path

Correct path

Merging classes Sperate/Same Location

Removed useless config directives

All NGINX files are now set to /tmp

Set more NGINX conf to /tmp/

Install custom NGINX the other way

Update install-nginx.sh

Fixing permissions

New method addRiskyTest required for phpunit >= 4

Installation is needed

Add shebang

Remove NginxSeparateLocation

Also support same location
Improve nginx docs and fix some bugs
Clean up nginx client and setup

- Expanded purge & refresh tests and new expired test
- Remove cache TTL in proxy_cache_valid (as suggested by @ddeboer)
- Custom log for better debug
- Improve installing nginx for testing
Merge remote-tracking branch 'origin/master' into nginx

Conflicts:
	.travis.yml
cleanup setup for nginx
cleaning up nginx doc
Merge remote-tracking branch 'origin/master' into nginx
adding license headers for nginx code
cleaning up hostname versus 127.0.0.1
cleanup doc a bit more
Merge pull request #49 from FriendsOfSymfony/nginx

Add Nginx support
Add tests for head request not in cache and vcl_pass configuration
Rewrite headers names, remove cooking filtering and fix typo