Initial addition of error handling support

Adds error reporting from server to client via the callback and
response. Use

in32_t response_status(BuxtonResponse response)

to obtain the error code, then use standard errno.h

Signed off by Brad Peters <brad.t.peters@intel.com>
Merge branch 'err_handling' of https://github.com/sofar/buxton into err_handling

Conflicts:
	src/core/daemon.c
	src/shared/backend.c
	src/shared/direct.c
	src/shared/hashmap.c
	src/shared/protocol.c