include: rename include/mod_starpu.f90 in include/starpu_mod.f90 and add function starpu_cpu_worker_get_count

Makefile.am

@@ -90,7 +90,7 @@ versinclude_HEADERS = 				\
 	include/starpu_thread_util.h		\
 	include/starpu_tree.h			\
 	include/starpu_simgrid_wrap.h		\
-	include/mod_starpu.f90
+	include/starpu_mod.f90
 
 nodist_versinclude_HEADERS = 			\
 	include/starpu_config.h