Move tests to relevant subprojects (#615)

- Moved test projects to the parent project they belong to
- Improved test stability/corectness
- Improved recursive directory deletion by safely ignoring current- and parent-directory entries.
- Update docs

TactilityFreeRtos/Tests/Source/PubSubTest.cpp

@@ -0,0 +1,36 @@
+#include "doctest.h"
+#include <Tactility/PubSub.h>
+
+using namespace tt;
+
+TEST_CASE("PubSub publishing with no subscriptions should not crash") {
+    PubSub<int> pubsub;
+    pubsub.publish(1);
+}
+
+TEST_CASE("PubSub subscription receives published data") {
+    PubSub<int> pubsub;
+    int value = 0;
+
+    auto subscription = pubsub.subscribe([&value](auto newValue) {
+        value = newValue;
+    });
+    pubsub.publish(1);
+
+    pubsub.unsubscribe(subscription);
+
+    CHECK_EQ(value, 1);
+}
+
+TEST_CASE("PubSub unsubscribed subscription does not receive published data") {
+    PubSub<int> pubsub;
+    int value = 0;
+
+    auto subscription = pubsub.subscribe([&value](auto newValue) {
+        value = newValue;
+    });
+    pubsub.unsubscribe(subscription);
+    pubsub.publish(1);
+
+    CHECK_EQ(value, 0);
+}