Setting api_version=cloud when Cloud=true (#532)

* Add method for add_space_permission (https://developer.atlassian.com/cloud/confluence/rest/api-group-experimental/#api-api-space-spacekey-permission-post). Needs some exception catching to deal with 400 errors, but it works!

* Cleanup JSON

* Removing id

* Might be good to use that cloud property to set api_version

* Documenting the cloud parameter

Co-authored-by: Darryl Lee <dlee@coyotecrk.com>

README.rst

@@ -38,6 +38,9 @@ Here's a short example of how to create a Confluence page:
 
     print(status)
 
+(Note that for Confluence Cloud, some API calls are different, so you'll 
+want to add cloud=True to the Confluence() connection.)
+
 And here's another example of how to get issues from Jira using JQL Query:
 
 .. code-block:: python

atlassian/rest_client.py

@@ -28,6 +28,8 @@ def __init__(self, url, username=None, password=None, timeout=60, api_root='rest
                 and '/wiki' not in url \
                 and self.__class__.__name__ in 'Confluence':
             url = self.url_joiner(url, '/wiki')
+        if (cloud == True):
+            api_version = 'cloud'
         self.url = url
         self.username = username
         self.password = password