Benchmark gravitation

See 0dbc299fdc4 for the cost of templatisation (between 15% and 20%).
Both before and after, the difference between native and CLR is about 10%.
Yep. All data correct. No idea why. Bear in mind that the absolute error is not large though, this is a near-circular orbit. I suspect some awful cancellation occurs (and I only copied 7 digits from HORIZONS).