Shaking while at the edge of the map has been completely eliminated. In
order to do this, comparison with tile height was also removed which
fixed a few outlier cases.
The main cause was viewport axis were only being set if it's respective
isometric axis was at the boundary, instead of either isometric axis.
Viewport no longer gets stuck which was related to the shaking in the
end. (#2875)
Refactored viewport_update_position. I moved
viewport_set_underground_flag above the bounds checking function since
it had no relation to it. (#996, #2589)
Scrolling on the map edge with arrow keys or mouse edge will now go the
same speed in both directions. (#2254)
Added changelog entry.