modules/world: add a basic solidity system

It'll make easier the solidity system and will reserve custom filter to 
specific objects.

examples/gameplay/moveplayer/actors/parent.lua

@@ -1,9 +1,9 @@
 local Base = require "gamecore.modules.world.actors.actor2D"
 local Parent = Base:extend()
 
-function Parent:new(world, type, x, y, w, h)
+function Parent:new(world, type, x, y, w, h, isSolid)
   self.scene = world.scene
-  Parent.super.new(self, world, type, x, y, w, h)
+  Parent.super.new(self, world, type, x, y, w, h, isSolid)
 end
 
 function Parent:draw()

examples/gameplay/moveplayer/actors/player.lua

@@ -3,7 +3,7 @@ local Parent = require(cwd .. "parent")
 local Player = Parent:extend()
 
 function Player:new(world, x, y)
-  Player.super.new(self, world, "player", x, y, 16, 16)
+  Player.super.new(self, world, "player", x, y, 16, 16, true)
 end
 
 function Player:update(dt)

gamecore/modules/world/actors/actor2D.lua

@@ -27,11 +27,11 @@ local Actor2D = Object:extend()
 -- INIT FUNCTIONS
 -- Initialise the actor and its base functions
 
-function Actor2D:new(world, type, x, y, w, h)
+function Actor2D:new(world, type, x, y, w, h, isSolid)
   self.type   = type or ""
 
   self:setManagers(world)
-  self:initPhysics(x, y, w, h)
+  self:initPhysics(x, y, w, h, isSolid)
 
   self:initKeys()
   self:register()
@@ -52,7 +52,7 @@ function Actor2D:setDebugColor(r,g,b)
   self.debug.b = b
 end
 
-function Actor2D:initPhysics(x, y, w, h)
+function Actor2D:initPhysics(x, y, w, h, isSolid)
   self.x      = x or 0
   self.y      = y or 0
   self.w      = w or 0
@@ -61,6 +61,8 @@ function Actor2D:initPhysics(x, y, w, h)
   self.xsp    = 0
   self.ysp    = 0
 
+  self.isSolid = isSolid or false
+
   self:setFilter()
 end
 
@@ -93,7 +95,11 @@ end
 function Actor2D:setFilter()
   -- Init the bump filter
   self.filter = function(item, other)
-    return nil
+    if (other.isSolid) then
+      return "touch"
+    else
+      return "cross"
+    end
   end
 end