Added getLastRequest and getLastResponse methods to Client class
Added Request::toString() method. Return request string representaion in curl style.
Added Request::toArray() method, toString() now return json encoded result of toArray()
Added Util::convertRequestToCurlCommand() method
Merge branch 'master' into client-last-request-response

Conflicts:
	test/lib/Elastica/Test/ClientTest.php
Set Request into ResponseException
Merge pull request #310 from munkie/client-last-request-response

Get last request and response from client