Add main.c file
Attempt to implement waiting system
Add freeing code for lists in the main function
Initializing fields in the newly created list to allow further sorting
The number of messages is always equal to the value of nMessages
Modify send_wait
Modify receive_wait and minor corrections to send_wait
Modify send_no_wait and receive_no_wait
The cleaning up of the Mailbox entry is actually done inside the messaging functions
No need to free pMessage memory which was not dynamically allocated
Create destroy_list function to manage the hypothetical removing of the lists