Moved the new packet buffer to the slave data structure to avoid errors when the packet is not fully received in a cycle.

Added the set_priorities() function.

Added a user buffer to allow reception of new data while processing the current one.
Solved a bug in handlding error for bulk and sync write operations.

When starting a new transmission, it does not wait for the previous one to finish (it must alrady have finished).

Solved a bug when receiving more than 256 bytes: the number of bytes received variable was an 8 bit integer.

Can devel

See merge request !13