Use realtimeify
Move to be shared code into files in lib/

Refine makefile to be usable with multiple executables
Add sync tool

Adds sync.c which contains a preliminary implementation of the
synchronisation process via control endpoint 0.
Update java2arduino-c

For no reason
Refactor main.exe

- Split get_time() into print_timespec(), print_time_device() and print_time_host()
- Get rid of sync_time()
- Allow for real precise wakeups in benchmark()
sync: use interrupt endpoint on independent interface

Also, use common header file/submodule for java2arduino and da.h for
sync constants (not yet included).
The latter is responsible for defining:
 - RTCSYNC_IF_CLASS
 - RTCSYNC_IF_SUBCLASS
 - RTCSYNC_IF_PROTOCOL
 - RTCSYNC_EP_ADDR (endpoint address + direction)