- split libio Makefiles for easier maintenance
- moved pcre.h to main include/ as it is currently a part
  of libio interface (in the future all such headers should
  be moved to libio/ and integrated...)

Now, libio components like comm, misc etc. should be as independent
as possible (from the rest of ircd and from each other), to allow
easy reuse in other software and to keep the interface clean.