A lot of minor changes

I changed a few physics parameters, enhanced the jumping experience but
removed a "protection" that prevented you from being able to push again
the side of a platform and therfore not falling. I changed the sleep
parameter because I felt that Box2D wasn't accurate enough.
I added the HistoryManager.
I changed Window to have all it's variable public, but you don't really
deal with them directly, you go through the WindowManager.
I also added the possibility to zoom, which simply zooms artificially
and isn't fully working yet.
Minor changes

I found a little bug in the iterator behavior, it's corrected.
I also took care to delete the tmpGameObjects that aren't useful.
Bug correction

I saw a few bugs in the orderGameObjects() function, so I cleaned that
up and realized the bugs were in our implementation of Llist.
I added a function setPositionInList() to set the "pos_in_list"
variable, instead of re-writting the same code every time.
I changed the z_index to be a uint16, and it has to be a mutiple of 2,
always. This is because of the way Box2D manages filtering.
MAJOR CHANGE: I changed the form of the hit box of the player -> now
it's two circles of radius 25px each, on top of each other. This is to
avoid getting stuck in certain places, and also to approach a little
better a human shape.
Lots of changes

Explained in the mapEditor repo.
Switch to SDL2

I switched to SDL2 for the possibility to have multiples windows.
I added the ctrl-z thing to respawn deleted objects (aka when you delete
an object you don't actually delete it, though you remove it's body,
therefore it's no longer physical)
I am using rapidXML now to parse our lib file, it's so much easier and
nicer. It is also really really fast, because it's made that way.

MAJOR CHANGE: I changed the way we create surfaces. Now a surface is
created ONCE from the file, and then a pointer is re-used for all the
objects having the same texture. It liberates a lot of memory and allows
us to have thousands of objects.

Need to change: We need to change the way we create the physical body
(and therfore we need a vector position, even if the body is NULL)
New Readme
New readme
SDL2 update

I updated SDL_image to work with SDL 2.0
I added a couple definitions like the size of a button or the scrolling
speed.
I think we should delete Properties, because I don't see where we're
using it.
Members of Surface (width and height) are now public.
ToolManager up and running!
Buttons -> new class that draw a button using an SDL_Renderer (the size
is defined in the definitions)
new readme
WOW LinkedList still buggy

One day it will be perfect, for now we still have some bugs, and I
correct them ;)
Small changes