Add HealpixNested.getNHash() method for easy access to number of 'cells'?

[BerryHoll]

If I understand correctly the way to get the number of cells, for a given depth is using:

Healpix.nHash(depth)

However, it would make sense to be able to get access to this value also from the HealpixNested object after construction, especially since it is already available as internal variable 'nHash'.
Could you add a simple accessor to the value by adding:

public long HealpixNested.getNHash() {
   return this.nHash;
}

[fxpineau]

Done.
Do you have other similar requests (before I make a new release)?