T-Engine 3.0.0alpha18 aka "The Immortal Fire"

Bug changes:
- Fill Traps spells will not craete stacks and stacks of traps
- Fix negative skill value
- When no abilities to display, do not load the abilities screen
- Defining flags on a building square in a map file works
- Random name generator now correctly use non defaults
- Fractal generator could sometimes crash, no more
- Fix the forced coords system when walking of the edge

Dungeon changes:
- New flag available for dungeons/levels to define number of traps/objects/...
  that will be generated if using the default generator.
  GENERATOR_GET_QUANTITY = function(type, k) return true, X end
  "type" is one of "traps", "objects_room", "objects_dun", "rubbles", "gold"
  "k" is the number that would be used to feed the rng to generate them.
  Return false to not handle the type, return true, 0 to not generate any

Gameplay changes:
- Flush key input when generating a level to avoid stupid deaths

Interface changes:
- No more 'N' key for abilities, they are now merged in the skill screen.
  It makes more sense as they both use skill points and it makes abilities
  more obvious to beginners. Also it allows abilities screen to benefit
  from the cancellation function
- Gaining a quest now displays the danger level

Monster changes:
- Some monsters can now resist pushback with the NO_PUSHBACK flag

Object changes:
- A new flag MONEY_PICKUP is available for money, if present it will
  be called to display the money pickup message and assign the gold.
  MONEY_PICKUP = function(amount, name)
    message("You have found "..amount.." whatever worth of "..name)
    return amount
  end
  You may wish to define it as a default flag for all your money
  in the default section of the moneys :)

Misc changes:
- Removed lots of dead code thanks to takkaria
- Store maintainance implemented. New flag STORE_MAINTAIN_TURNS. If not present
  stores will maintain every 1000 turns. If present they will maintain
  every STORE_MAINTAIN_TURNS turns. If set to 0 it will NEVER maintain.
  Set it to 0 for houses
