gx_simulator

This is a major release in which: 1) the xray_tt_albedo.pro and xray_tt_albedo_arr.pro have been updated to allow for arbitrary distances between the Sun and Observer and arbitrary spacecraft line of sights; and 2) The gxisogauss surface object have been introduces, along with the gx_display_manager.pro GUI utility, which may be used to generate, manage, and display such iso gauss surfaces.