Expose additional properties for Gitlab objects

* url: the URL provided by the user (from config or constructor)
* api_url: the computed base endpoint (URL/api/v?)

Fixes #474

gitlab/__init__.py

@@ -78,6 +78,7 @@ def __init__(self, url, private_token=None, oauth_token=None, email=None,
 
         self._api_version = str(api_version)
         self._server_version = self._server_revision = None
+        self._base_url = url
         self._url = '%s/api/v%s' % (url, api_version)
         #: Timeout to use for requests to gitlab server
         self.timeout = timeout
@@ -164,8 +165,19 @@ def __setstate__(self, state):
                                           self._api_version)
         self._objects = objects
 
+    @property
+    def url(self):
+        """The user-provided server URL."""
+        return self._base_url
+
+    @property
+    def api_url(self):
+        """The computed API base URL."""
+        return self._url
+
     @property
     def api_version(self):
+        """The API version used (3 or 4)."""
         return self._api_version
 
     def _cls_to_manager_prefix(self, cls):