squashed commits

squash: use kString_text() macro
squash: pickup all libevent API interface in C
squash: event_free() will call in cevent_Free()
squash: rename local variable
squash: confirmed cevent_base.get_supported_methods() by get_supported_methods.k
squash: implemented all of event_base class
squash: implemented all of event_config class
squash: add libevent version comparison for support APIs
squash: implement all of include/event2/event.h API
Merge pull request #416 from tosnoz/libevent_event_h

implemented all of event.h APIs