Add Catch framework for testing embedding support and C++-side features
At this point, there is only a single test for interpreter basics.
Apart from embedding itself, having a C++ test framework will also
benefit the C++-side features by allowing them to be tested directly.
diff --git a/tests/test_embed/catch.cpp b/tests/test_embed/catch.cpp
new file mode 100644
index 0000000..f79fe17
--- /dev/null
+++ b/tests/test_embed/catch.cpp
@@ -0,0 +1,5 @@
+// Catch provides the `int main()` function here. This is a standalone
+// translation unit to avoid recompiling it for every test change.
+
+#define CATCH_CONFIG_MAIN
+#include <catch.hpp>