New "module" proc.c/proc.h for generic process handling

New "module" proc.c/proc.h for generic process handling

The new "module" proc.c is used for functions dealing with child
processes. At the moment, it is only used by the asynchronous resolver.

All the functions already implemented habe been migrated from the
resolver code base, and the rest of the ngIRCd source code has been
adepted to the new namespace and calling conventions.

The goal is to develop "generic" process handling functions that can
be used for other purposes as well, e.g. running processes on client
connects etc.