Work in progress, but this is to cover some exploratory changes to switch to libevent2. The end of this may or may not result in immediate merging of this, but it will help define the scope of changes necessary to link against libevent2.
simplehttp changes for libevent2
more changes for libevent2; expose simplehttp_current_base
short summary is this: libevent2 transition is pretty straight forward.
A few methods are depreciated, and we could continue using them, but we should switch to new methods that take an explicit event_base (exposed now as simplehttp_event_base). Other stuff that are old structures which aren't ideal to use have *_compat.h includes or *_struct.h includes that just need to be added; using those makes things brittle as it introduces binary incompatibility, but there isn't any other downside to using them.