wldbg: move struct wldgb definition into wldbg.h

We need it accessible from other files and this wldbg.h won't
be distributed anyway.
wldbg: rename run to wldbg_run and add wldbg_init

Let's be at least a little bit consistent
add support for debugging

very simple, just dbg(msg, ...) macro and ifdbg(cond, msg, ...) macros
that will be run when WLDBG_DEBUG env is set. It can be turned out
by --diable-debug
add interactive and passes files with function skeletons

Initial commit for some cmd parsing and interactive behaviour