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

Modules/crypt-module/tests/source/hash_test.cpp

@@ -0,0 +1,28 @@
+#include "doctest.h"
+#include <crypt/hash.h>
+#include <cstring>
+
+TEST_CASE("djb2_str of an empty string returns the DJB2 seed value") {
+    CHECK_EQ(djb2_str(""), 5381u);
+}
+
+TEST_CASE("djb2_str produces the well-known DJB2 hash for a string") {
+    CHECK_EQ(djb2_str("hello"), 261238937u);
+}
+
+TEST_CASE("djb2_str is deterministic for the same input") {
+    CHECK_EQ(djb2_str("tactility"), djb2_str("tactility"));
+}
+
+TEST_CASE("djb2_str produces different hashes for different input") {
+    CHECK_NE(djb2_str("tactility"), djb2_str("Tactility"));
+}
+
+TEST_CASE("djb2_data of an empty buffer returns the DJB2 seed value") {
+    CHECK_EQ(djb2_data("", 0), 5381u);
+}
+
+TEST_CASE("djb2_data matches djb2_str for the same bytes") {
+    const char* text = "tactility";
+    CHECK_EQ(djb2_data(text, strlen(text)), djb2_str(text));
+}