[PHP] add debug switch

[wing328]

• add debug switch to Configuration
• allow curl debugging
• better exception handling

PHP tests are good.

Here is an example of the debug log:

[DEBUG] HTTP Request body  ~BEGIN~

~END~
* Hostname was NOT found in DNS cache
*   Trying 54.69.214.189...
* Connected to petstore.swagger.io (54.69.214.189) port 80 (#0)
> GET /v2/pet/10005 HTTP/1.1
User-Agent: PHP-Swagger
Host: petstore.swagger.io
Accept: application/json
Content-Type: application/json

< HTTP/1.1 200 OK
< Access-Control-Allow-Origin: *
< Access-Control-Allow-Methods: GET, POST, DELETE, PUT
< Access-Control-Allow-Headers: Content-Type, api_key, Authorization
< Content-Type: application/json
< Connection: close
* Server Jetty(9.2.7.v20150116) is not blacklisted
< Server: Jetty(9.2.7.v20150116)
< 
* Closing connection 0
[DEBUG] HTTP Response body ~BEGIN~
{"id":10005,"category":{"id":10005,"name":"test php category"},"name":"PHP Unit Test","tags":[{"id":10005,"name":"test php tag"}]}
~END~