according to doxygen only
  "sound", "modem", "monitor", "filter"
are allowed. Use sound as this is the most appropriate

also plasma-pa hides virtual devices by default.

flag them as hardware since to the user this virtual card behaves like
that. It is not some kind of filter or secondary output

- config.h is now search for under PULSE_DIR
- Location of config.h can be specified explicitly with PULSE_CONFIG_DIR
- Extra warning if PULSE_DIR appears to be invalid

Closes: #36

snprintf requires malloc before copying strings. I didn't do enough test the case
when socket names were not given via environment variable.

and remove CHANSRV, use the shorter name

now this module no longer depends on xrdp headers.