channel/add - Creates a new channel.

Method parameters:
channel_name - The name of the channel.
public - Whether the channel should be marked as public.
receive_notifications - Whether the channel owner should receive notifications.

Returns a JSON document of the following format:
<number> - The ID of the newly created channel.

Expected errors:
ENTER_CHANNEL_NAME - The name is empty.
INVALID_CHANNEL_NAME - The name is invalid.
CHANNEL_NAME_TOO_SHORT - The channel name is shorter than 6 characters.
CHANNEL_ALREADY_EXISTS - A channel with the same name already exists.