API update: promote xy_site and hex_orientation to top-level module

Recent work with the Kane-Mele model has made clear that we need quite
often to manually generate the hoppings, as well as defining a custom
unit-cell, already at the unit-vector level. It follow that both types
xy_site and hex_orientation are needed for a fairly basic usage.

Since we change API (even if in a non-breaking fashion) we should soon
bump the version. Though I'll wait until I update the README.

src/honeytools.f90

@@ -11,9 +11,9 @@ module honeytools
    implicit none
    private
 
-   public :: xy_lattice, xy_print, xy_shells, xy_nn_hop, xy_nnn_hop
+   public :: xy_site, xy_lattice, xy_print, xy_shells, xy_nn_hop, xy_nnn_hop
    public :: xy_nearest_neighbors, xy_next_nearest_neighbors
-   public :: unit_cell, armchair, zigzag ! to generate layouts
+   public :: unit_cell, hex_orientation, armchair, zigzag ! to generate layouts
    public :: get_supercell, get_triangle, get_flake, get_stripe, get_sublattice
 
 contains