First part of the board bringup: power and clock.

- atusd/ERRATA: variations of the circuit being debugged from the design
- tools/Makefile, tools/try.c, tools/lib/atusd.c: user-space tool to enable
  the board and (in the future) establish communication
- atusd/sim/clk.sch: simulation of CLK attenuation circuit with capacitative
  load from scope probe

atusd/tools/try.c

@@ -0,0 +1,14 @@
+struct atusd_dsc;
+
+
+int main(void)
+{
+	struct atusd_dsc *dsc;
+	char tmp;
+
+	dsc = atusd_open();
+	read(1, tmp, 1);
+	atusd_close(dsc);
+
+	return 0;
+}