= Yugine Engine

The yugine essentially is made of a sequence of levels. Levels can be
nested, they can be streamed in, or loaded one at a time. Levels are
made of levels.

Different "modes" of using the engine has unique sequences of level
loading orders. Each level has an associated script file. Level
loading functions call the script file, as well as the level file. The
level file can be considered to be a container of objects that the
associated script file can access.

.Game start

* Engine scripts
* config.js
* game.lvl & game.js

.Editor

* Engine scripts
* config.js
* editor.js

.Editor play

* F5 debug.lvl
 - Used for custom debug level testing. If doesn't exist, game.lvl is loaded.
* F6 game.lvl
* F7 Currently edited level

While playing ...
* F7 Stop

.Level model
The game world is made up of objects. Levels are collections of
objects. The topmost level is called "World". Objects are spawned into
a specific level. If none are explicitly given, objects are spawned
into World. Objects in turn are made up of components - sprites,
colliders, and so on. Accessing an object might go like this:

World.level1.enemy1.sprite.path = "brick.png";

To set the image of enemy1 in level 1's sprite.

.Textures & images
A sprite is a display of a specific texture in the game world. The
underlying texture has values associated with it, like how it should
be rendered: is it a sprite, is it a texture, does it have mipmaps,
etc. Textures are all file based, and are only accessed through the
explicit path to their associated image file.

.Scripting

Levels and objects have certain functions you can use that will be
called at particular times during the course of the game running.

setup
  Called once, when the object is created.

start
  Called once when the gameplay is simulating.

update(dt)
  Called once per frame, while the game is simulating

physupdate(dt)
  Called once per physics step

stop
  Called when the object is destroyed, either by being killed or otherwise.

.Collider functions
Colliders get special functions to help with collision handling.

collide(hit)
  Called when an object collides with the object this function is on.

"hit" object
  normal - A vector in the direction the hit happened
  hit - Object ID of colliding object
  sensor - True if the colliding object is a sensor
  velocity - A vector of the velocity of the collision