still working on error handling

pyownet.protocol.Error hierarchy reorganized

better code for fetching errcodes from owserver
better OwnetProxy init logic
release 0.7.1
examples directory added
bugfix for socket methods

1) check for exceptions raised by socket.shutdown
2) add MSG_WAITALL flag to socket.recv

code tested on GNU/Linux and OSX
better error messages
Merge branch 'master' into sensors