building.md: added info about AoEHD now being supported.
add debug overlay grid, togglable with F4
Merge pull request #138 from franciscod/debug_overlay_grid

game: add debug overlay grid, togglable with F4
Add .desktop file and generate placeholder icon.
Merge pull request #81 from boombatower/desktop-file-plus-icon

Add .desktop file and placeholder icon.
Merge remote-tracking branch 'upstream/master'
unit attribute system