optimizing message creation and check return of function ngx_http_push_stream_apply_text_template calls for errors

fix memory leaks when saving channels on a rbtree with ids which collides, problem inherited from Nginx and reported by Lanshun Zhou

removing conditional use of ngx_time_update function, versions 0.7.x are no longer supported, since version 0.2.5

fix bug which make subscribers unresponsive on some race conditions when the workers does not receives an alert

adding tag and time available at message template, and make possible pass these values whithout set headers