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

Tactility/Tests/Source/StringTest.cpp

@@ -0,0 +1,63 @@
+#include "doctest.h"
+#include <Tactility/StringUtils.h>
+
+// region split
+
+TEST_CASE("splitting an empty string results in an empty vector") {
+    auto result = tt::string::split("", ".");
+    CHECK_EQ(result.empty(), true);
+}
+
+TEST_CASE("splitting a string with a single token results in a vector with that token") {
+    auto result = tt::string::split("token", ".");
+    CHECK_EQ(result.size(), 1);
+    CHECK_EQ(result.front(), "token");
+}
+
+TEST_CASE("splitting a string with multiple tokens results in a vector with those tokens") {
+    auto result = tt::string::split("token1;token2;token3;", ";");
+    CHECK_EQ(result.size(), 3);
+    CHECK_EQ(result[0], "token1");
+    CHECK_EQ(result[1], "token2");
+    CHECK_EQ(result[2], "token3");
+}
+
+// endregion split
+
+// region join
+
+TEST_CASE("joining an empty vector results in an empty string") {
+    std::vector<std::string> tokens = {};
+    auto result = tt::string::join(tokens, ".");
+    CHECK_EQ(result, "");
+}
+
+TEST_CASE("joining a single token results in a string with that value") {
+    std::vector<std::string> tokens = {
+        "token"
+    };
+    auto result = tt::string::join(tokens, ".");
+    CHECK_EQ(result, "token");
+}
+
+TEST_CASE("joining multiple tokens results in a string with all the tokens and the delimiter") {
+    std::vector<std::string> tokens = {
+        "token1",
+        "token2",
+        "token3",
+    };
+    auto result = tt::string::join(tokens, ".");
+    CHECK_EQ(result, "token1.token2.token3");
+}
+
+TEST_CASE("joining with empty tokens leads to an extra delimiter") {
+    std::vector<std::string> tokens = {
+     "token1",
+     "",
+     "token2",
+    };
+    auto result = tt::string::join(tokens, ".");
+    CHECK_EQ(result, "token1..token2");
+}
+
+// endregion join