Add jet, surface and fixed-patch tests and runnable examples

tests/unit/cpp/slot_profile.cpp

@@ -0,0 +1,10 @@
+#include <cmath>
+#include <cstdio>
+#define __device__
+#define __forceinline__ inline
+#include "boundary/planar_velocity.cuh"
+
+int main() {
+    for (unsigned x=0; x<NX; ++x)
+        printf("%.9g\n", bottom_wall_normal_velocity(x));
+}