Updated License

Changed license from GPL to zlib.
Added support for Lua 5.1

Replaced instances of arg with {...}. This means that earlier versions
of Lua will no longer be supported.
Added secs.queryfirst() function

Returns the first entity of the provided type for the current scene.
Removed secs.factory()

Since factories do not gain any benifit from being explicitely part of
the entity component system rather than being normal functions, it has
been removed.
Removed priority property from systems

Systems are now called in the order in which they are initialized. Found
this to be less cumbersome.
Complete rewrite

* All functions now require a self reference (i.e. colon operator)
* Functions that do not construct objets now use lower camel case.
* Functions that construct objets now use upper camel case.
* Added more detailed comments and documentation.
* Various refactoring.
* Updated readme.
Changed attach() and Entity() interface

Entity() and attach() now take a table of component data where the key
is the component name and the value is a table of component values.

i.e. secs:attach(entity, { componentName = { value = 1 }})
Replaced the entityType with simple queries

Removed EntityType() and changed query() and queryFirst() to accept a
whitespace-separated string of component names. Any time a query is
made, an entity type is automatically created in the background to cache
and manage the results for that query.
Added System() and removed RenderSystem() and UpdateSystem()

System takes a table that contains either an update() function or draw()
function. Tables that contain an update() function are added to the list
of update systems, while tables that contain a draw() function are added
to the list of draw systems.

Systems is intended to replace UpdateSystem() and RenderSystem().
Changed tabs to spaces
Changed return value to table instead of function

When the module is required by another file, a table will be returned
instead of a function. This is to keep it more consistant with other
modules.