When an entity dies, it is immediately removed from the current selection
Only select entities that can be selected

It is used to attach certain response (for example graphical or sound
effects) with various events of the World

With an example of Blink

And use more precise duration types

And fix the fog for that, as well

Use the Entity class everywhere, instead
fix #2803

The world is now isometric. fix #2277
Simplify TurnHandler. fix #2724 #2704

The world and game modules are now more decoupled. fix #2587

Implement a debughud. fix #2417

Better separation of modules (network does not know about world anymore, for
example).
Ref #2587

Do not yet properly draw the units at their correct position, though

Also fix the selection, properly handling a mouse selection containing
buildings etc. Also fix the archive building image.

Parse a yaml file containing various informations about the game and use
them in the world and gui modules.

Entity should then be inherited in the Building class as well.

Can be used to pass a spell id, a page id, etc.

The page is reseted when the action is executed or when the selection is
modified.

Actions for the selected entity are displayed as buttons in it, when
clicking on one it changes the behaviour of the left click, as well as the
cursor appearance.

Lets you click or shift click on the entities in the hud to
select/unselect some of them.
Implements a tab system, to select up to 240 entities at once.

Use mpfr for world positions and heights.
Add a visible hud
Change some little camera/selection/movement stuff
And maybe other things.

A client can now join a game that was started, and participate normally,
as if it was there from the start.
Next commit should fix the issue of a leaving client, make the game pause
for everyone else, if it left before confirming an action that was sent
to it.