Use primitive array in Point instead of List

[jush]

Avoid using List<Double> for Point. Instead use double [].

Moreover, expose accessors to the flatten structure.

This change improves memory usage significantly:

Before: using List	After: using double []
3M list of points take 286,1MB	3M double [] points take 45,8MB

[dmitry-novikov]

Should we just pre-fill all array with NaN and then set valid values on top of it during i cycle?

[jush]

I think that would result in unnecessary CPU cycles for the non-NaN future ones.

I don't have hard numbers but I would imagine that if the points have altitude I guess most of them will have it. I think (again no evidence) the pattern will be that either there's altitude for all points or there's none.

Or is there a fast way to pre-fill with NaN? without iterating one by one?