mccmd 0.3: new C client, better server logging

- server now logs each command along with the client's ip address and port
- made MessageReciever identify itself as 'mccmd@clienthost:clientport'
  instead of just 'mccmd'
- moved ConnectionHandler out of SocketListenerThread.java and into its own
  file, ConnectionThread.java. Sort of a hack to make writing the Makefile
  easier (SocketListenerThread.java -> SocketListenerThread.class +
  SocketListenerThread$ConnectionHandler.class is not an easy thing to predict
  in a Makefile), but it improves readability so whatever.
- replaced crappy python client with a shiny new C client
- systemd unit is no longer included in the arch PKGBUILD
  (tweak it and put it in /etc/systemd/system/ yourself!)
- swapped build system from kludgey shell scripts to Makefiles
- update README to reflect changes