Implement adaptive resampling based on effective sample size

[jbrodovsky]

        // TODO: Implement adaptive resampling based on effective sample size

In file core/src/particle.rs

strapdown-rs/core/src/particle.rs

Line 358 in 67aa858

particle.nav_state.velocity_down += rand_distr::Normal::new(0.0, self.process_noise[5])