Extremely basic integration of wvtest for testing.

And move test scripts into t/ subdir to keep things clean.

As part of that, make sure redo adds itself to the PATH on startup so that
subscripts can find it.

t/hello.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int main()
+{
+    printf("hello, world!\n");
+    return 0;
+}