* Having a configuration object will allow future extensions without
  a change of interface to cdiPioInit.
* Also move code to translate I/O mode string vs. integer into library.

* The function is correspondingly renamed to reflect the narrower
  functionality.

* Now that setting up of communications has been consolidated in
  cdiPioCommInit, the initial callback of cdiPioInit can now be
  called regardless of backend mode.

* Every server now serves a subset of the clients only.

* The previous construct could result in a double-free.

* This way no static variables are needed,
  unless the source is compiled with C++.

* This will later allow appending to the (resized) buffer.

* This moves the check and conversion to lower case to the public
  interface and simplifies internals.

* If pio_write -s switch is used, the effective seed is printed.