New feature: getAmps

[TysonRayJones]

void getAmps(QubitRegister qureg, long long int startInd, long long int numAmps, REAL** reals, REAL**imags);

This mallocs two REAL lists (for the real and imaginary components) and populates them with amplitudes of the statevector in the given index range (startInd to startInd+numAmps).
In distributed mode, this involves a reduction.

Example use:

REAL *reals, *imags;
getAmps(qureg, 10, 500, &reals, &imags);
free(reals);
free(imags);

Alternatively, forcing the user to alloc (so that they may pass arrays) is ok too

[TysonRayJones]

and the density matrix getDensityAmps of course