Add clean and veryclean targets to Makefile

And add gitignore file.

.gitignore

+carra_obsoul.main.o
+carra_obsoul.main.x
+ext_lam_synop.o

Makefile

@@ -10,3 +10,11 @@ carra_obsoul.main.x:	$(OBJ)
 
 %.o:	%.f90
 	$(FC) $(FC_FLAGS) -c $<
+
+# Utility targets
+.PHONY: all clean veryclean
+
+clean:
+	rm -f *.o *.mod *.MOD
+veryclean: clean
+	rm -f *.x