Add registerfile implementation

Registerfile for use with rs485 registers. For know I added
one large (23 registers), but maybe its better to have one
for input and one for output later on. Also it might require
more than one reader and writer in future (more readers are
simple)

Signed-off-by: Thommy Jakobsson <thommyj@gmail.com>
Merge branch 'master' of github.com:thommyj/slotcar