Add tests for sqrt, fmod (#612) and floating point printf/scanf (#1179)

Author: igrr

tests/device/test_newlib/test_newlib.ino

@@ -0,0 +1,30 @@
+#include <BSTest.h>
+BS_ENV_DECLARE();
+
+
+void setup()
+{
+    Serial.begin(115200);
+    BS_RUN(Serial);
+}
+
+TEST_CASE("Floating point formatting works", "[newlib]")
+{
+    char buf[16];
+    const float val = 0.02300;
+    snprintf(buf, sizeof(buf), "%.05f", val);
+    CHECK(String(buf) == "0.02300");
+    float res;
+    sscanf(buf, "%f", &res);
+    CHECK(res == val);
+}
+
+TEST_CASE("#612 fmod and sqrt work", "[newlib]")
+{
+	CHECK(fabs(fmod(2.0, 1.5) - 0.5) < 1e-6);
+	CHECK(fabs(fmod(-10, -3) - (-1.0)) < 1e-5);
+}
+
+void loop()
+{
+}