add implementation for the key-value store

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
add a memory allocator inside the data store

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
use char instead of uint8_t for interface

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
implemented the messaging code for data store operations

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>