irccmd.c: Don't load/reference Lua BitOp.
Make irccmd a Lua library instead.

src/irccmd.c:
  adapt code to be usable as a library (pass lua_State *L argument, etc)
  Removed debug code that is no longer relevant.
irccmd.lua changes

Call socket init/cleanup code as was done in C.
Adapt "arg" to what irccmd_startup() expects.
Rename irccmd.so to irccmd_internal.so.