make name the parameter, with hostname as alias

name is used throughout Ansible, it's the "standard". This change
applies that standard to the add_host routine and updates the docs to
reflect that. Related to https://github.com/ansible/ansible/pull/3254

inventory/add_host

@@ -10,6 +10,7 @@ description:
 version_added: "0.9"
 options:
   name:
+    aliases: [ 'hostname' ]
     description:
     - The hostname/ip of the host to add to the inventory, can include a colon and a port number.
     required: true     
@@ -23,10 +24,10 @@ author: Seth Vidal
 
 EXAMPLES = '''
 # add host to group 'just_created' with variable foo=42
-- add_host: hostname=${ip_from_ec2} groups=just_created foo=42
+- add_host: name=${ip_from_ec2} groups=just_created foo=42
 
 # add a host with a non-standard port local to your machines
-- add_host: hostname='${new_ip}:${new_port}' 
+- add_host: name='${new_ip}:${new_port}' 
 
 # add a host alias that we reach through a tunnel
 - add_host: hostname=${new_ip}