add 'dogecoin_node_group_event_loopbreak(dogecoin_node_group)'

[UsaRandom]

i have the spv node event_loop dogecoin_node_group_event_loop() running on a separate thread but i've had issues getting the event_loop call to always return (exit) using just dogecoin_node_group_shutdown() (symptomatic of another issue?)

all the peers disconnect, but since the event_loop call doesn't always return, sometimes my thread hangs (and apparently you can't just kill threads now in dot-net...)

the new function dogecoin_node_group_event_loopbreak() wraps event_base_loopbreak(), which makes the event_loop call return.

event_base_loopbreak

Abort the active event_base_loop() immediately.

event_base_loop() will abort the loop after the next event is completed; event_base_loopbreak() is typically invoked from this event's callback. This behavior is analogous to the "break;" statement.

Subsequent invocations of event_base_loop() will proceed normally.

[edtubbs]

Thanks! Have a look at #207 for a related update. It addresses the exit issue and should resolve your event loop problem.