update sample/06_hardcore_boson_triangular

[yomichi]

Now calculate the Fourier transform of densities $\langle n_i \rangle$ and density-density correlations along the x-axis $C(x) = \sum_r \langle n(r) n(r+x)$ as well as the density-density correlations of all the pairs of sites $\langle n_i n_j \rangle$
The tutorial (manual) is also updated.