[communication] Creates new functions to optimize the use of the incoming buffer (avoid creating temporary copies of messages, uses pointers instead).
* modifies sb_pushInBufLast prototype to avoid the need to create a temporary sMsgIf structure.
*creates sb_getInBufFirst to ge the pointer to the message to read (and avoid useless copy).
[communication] Solves the problem of "no message received while sending" on Xbee, corrects one mistake in a comment.