log.c: include stdarg.h to avoid compile warning on macosx
Add a configure script
Makefile.in: move -shared into LDFLAGS
Makefile.in: create $(LIBDIR) if needed
Remove echo.h and poller.h

I am about to commit code that automatically generates the C
header that contains libneubot interface.
Rename openbsd_strtonum neubot_strtonum
echo.c poller.c: switch to libneubot.h
echo.c poller.c: more consistent names for private functions

Always prefix the name of a function with the name of the structure
that owns such function.

Do not add the underscore suffix to private functions.
Add libneubot.json that describes libneubot interface
add gen_header that generates libneubot.h
Add gen_py that generates libneubot.py
configure: autogenerate libneubot.h and libneubot.py
Makefile.in: install libneubot.h too
libneubot.h -> neubot.h

Based on the observation that, e.g., libevent uses event.h.
gen_py: tweak the name of callbacks
gen_py: make sure argtypes is always a tuple
gen_py: convert void * to py_object
add test_echo.py: test for the code in echo.c
libneubot: more tidy to pass NeubotPollable to callbacks
libneubot: add NeubotPollable_poller()