remove global references to main module conf, ping and long polling timeout messages, and shared memory zones

add push_stream_timeout_with_body directive to indicate whether send a full message on timed out long polling connections, or not

start etag as 1 to avoid concurrency problems when subscriber connects on the same second of a message is published

change the publish message action through a WebSocket connection to add the message to all subscribed channels

make possible post messages in some channels or delete them at once specifying their ids on push_stream_channels_path diretive separated by a slash

avoid reapply formatter to header, message or footer template when inside an if on event source mode

normalize use of backtrack, last_event_id and if_modified_since/if_none_match values to get old messages on all subscriber modes

removed push_stream_content_type directive, use default_type Nginx directive to set the value, except on JSONP and Event Source modes

removed push_stream_keepalive directive, let Nginx decide when to use keepalive and how many requests accept using keepalive_* directives