States fix

No more specific classes for every game state.
game.lua, title.lua asn they call in main.lua
add entities module

See #8.
use entities everywhere
clear entities on initialization
Merge branch 'master' into entities

* master:
  States fix
Merge branch 'entities'

Close #8.

* entities:
  clear entities on initialization
  use entities everywhere
  add entities module
Merge branch 'master' into emitters

* master:
  clear entities on initialization
  use entities everywhere
  add entities module
  States fix
emitters are entities too