Renamed directory nmon to pqnmon
Created PqIostatAix and PqIostatLinux

PqIostatAix and PqIostatLinux are subclasses of PqIostat. PqIostat
provides common functionality and interface.
TODO: harmonize method invocations and have program decide whether
to use AIX or Linux version. On the other hand: output for AIX /
Linux is not congruent?...
Same interface for PqIostat and PqNmon

Adapted PqIostat such that it can called with the same interface
for processing as PqNmon, i.e. process(input_files, out_dir).
This makes it simpler to include both into PqProc.
PqProc - initial version of a daemon process

Initial version of a daemon process monitoring input directories
for newly arrived nmon or (AIX) iostat files.
TODO: Generic AIX/Linux; multithreading (?needed?), Ruby-GC (?)