HAL: added Printf test sketch

for testing new non-asm printf code

libraries/AP_HAL/examples/Printf/Makefile

@@ -0,0 +1 @@
+include ../../../../mk/apm.mk

libraries/AP_HAL/examples/Printf/Printf.pde

@@ -0,0 +1,61 @@
+#include <AP_HAL.h>
+#include <AP_HAL_AVR.h>
+#include <AP_HAL_AVR_SITL.h>
+#include <AP_HAL_PX4.h>
+#include <AP_HAL_Empty.h>
+#include <AP_Common.h>
+#include <AP_Baro.h>
+#include <AP_ADC.h>
+#include <GCS_MAVLink.h>
+#include <AP_Compass.h>
+#include <AP_Declination.h>
+#include <SITL.h>
+#include <Filter.h>
+#include <AP_Param.h>
+#include <AP_Progmem.h>
+#include <AP_Math.h>
+
+const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;
+
+void setup(void) {
+    hal.console->println_P(PSTR("Starting Printf test"));
+}
+
+static const struct {
+    const char *fmt;
+    float v;
+    const char *result;
+} float_tests[] = {
+    { "%f", 3.71f, "3.710000" },
+    { "%.1f", 3.71f, "3.7" },
+    { "%.1f", 3.75f, "3.8" },
+    { "%.2f", 3.75f, "3.75" },
+    { "%.7f", 3.75f, "3.7500000" }
+};
+
+static void test_printf(void)
+{
+    uint8_t i;
+    char buf[30];
+    uint8_t failures = 0;
+    hal.console->printf("Running printf tests\n");
+    for (i=0; i<sizeof(float_tests)/sizeof(float_tests[0]); i++) {
+        hal.util->snprintf(buf, sizeof(buf), float_tests[i].fmt, float_tests[i].v);
+        if (strcmp(buf, float_tests[i].result) != 0) {
+            hal.console->printf("Failed float_tests[%u] '%s' -> '%s'\n", 
+                                (unsigned)i, 
+                                float_tests[i].fmt,
+                                buf);
+            failures++;
+        }
+    }
+    hal.console->printf("%u failures\n", (unsigned)failures);
+}
+
+void loop(void) 
+{	
+    test_printf();
+    hal.scheduler->delay(1000);
+}
+
+AP_HAL_MAIN();