Allow complete URL in get method

The get method always prepends the baseurl before the requests path.
A check was added to allow for full URLS (starting with baseurl), for following
pagination links.
Added the perPage property for Github pagination

The api client supports the per_page github parameter for api calls.
Default is NULL and lets github decide the default (currently 30).

$client->setPerPage()
Added the ResultPaginator (incomplete)

This is the first pass at adding a paginator class for github API requests.
It only works with fetchAll() at the moment, to demonstrate the usage.

Currently:
$paginator = new \Github\ResultPaginator( \Github\Client [client] );
$paginator->fetchAll( [api], [method], [parameters] );

Todo's include:
Paginator is not complete for all possible headers Next, Last, Previous, First
apiClient should be able to return a paginator (i.e. $client->getPaginator() )
CacheHttpClient does not work (does not return Link headers)
removed debug