Documentation for Planner::new() does not mention power of two requirement

[HEnquist]

The new() function for the planner panics if the length is not a power of two:

PhastFT/src/planner.rs

Line 38 in 01aed51

assert!(num_points > 0 && num_points.is_power_of_two());

But this is not mentioned in the docstring:

PhastFT/src/planner.rs

Line 36 in 01aed51

/// Panics if `num_points < 1`

[HEnquist]

The same problem is in the fft() method here:

PhastFT/src/lib.rs

Line 29 in 01aed51

/// Panics if `reals.len() != imags.len()`