o support for selecting event backends by their features, and for querying the features of a backend.
o change failing behavior of event_base_new_with_config: if a config is provided and no backend is selected, return NULL instead of aborting.
o deliver partial data to request callbacks when chunked callback is set even if there is no chunking on the http level; allows cancelation of requests from within the chunked callback; from Scott Lamb.
+ o allow min_heap_erase to be called on removed members; from liusifan.
Changes in 1.4.0:
o allow \r or \n individually to separate HTTP headers instead of the standard "\r\n"; from Charles Kerr.