+ * Introduce typed tasks. Specify its kind and cost at creation.
+ At scheduling, just give where it should be placed, and the cost
+ for each involved resource is automatically computed.
+ Existing constructors so far (more to come of course):
+ - SD_task_create_comm_e2e() for end-to-end communication
+ - SD_task_create_comp_seq() for sequential computation
+ Use SD_task_schedulev() / SD_task_schedulel() to schedule them.
+ * new function SD_task_dump() for debuging display
+ * new function SD_task_dotty(task,FILE*) writing to file the info
+ about the task in dotty format