add tests folder and run-tests script

tests/.gitignore

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+test???

tests/test001.jtl

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+
+C("#include <stdio.h>");
+
+C("int main(int argc, char *argv[])");
+C("{");
+
+    C("printf(\"Hello, World!\\n\");");
+    C("return 42;");
+
+C("}");

tests/test001.out

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+Hello, World!