Existing conflict style is the local default ("merge", most
likely). `diff3` is a lot more informative as it provides the common
ancestor's code for the hunk, which helps see how the two branches
diverged and thus resolve the conflict.
Even better would be zdiff3 but that's a bit too recent...
Fixes#619
* Adds a changelog page, linked from the main, with content
automatically loaded from the source. To avoid conflicts, each entry
is its own file and entries are grouped by the month during which
the update will (probably) be deployed
* The last group (most likely "last update") doesn't have a title, the
rest do.
* Add changelog entries from the last update so it's not too empty.
* Also update the layout for the alerts a bit: remove bottom margin to
reduce loss of whitespace.
