Convert generated levels to walls

Add support for converting generated levels to walls, and merge one into
the entity map at the beginning of the game.

There's nothing here that guarantees the character ends up *inside* the
level though (they almost always don't) so that'll have to be slotted
into the level generation process.

xanthous.cabal

@@ -4,7 +4,7 @@ cabal-version: 1.12
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: e01963f3bf85136fe2b6993775d225999898d4c478efef6f917056f726d72e33
+-- hash: 3fbeb53b2706e3f0186fa3c80619a166f64eb52cf045006ac993074fa7f3e9d1
 
 name:           xanthous
 version:        0.1.0.0
@@ -35,11 +35,13 @@ library
       Xanthous.Data
       Xanthous.Data.EntityMap
       Xanthous.Entities
+      Xanthous.Entities.Arbitrary
       Xanthous.Entities.Character
       Xanthous.Entities.Creature
+      Xanthous.Entities.Draw.Util
+      Xanthous.Entities.Environment
       Xanthous.Entities.Raws
       Xanthous.Entities.RawTypes
-      Xanthous.Entities.SomeEntity
       Xanthous.Game
       Xanthous.Game.Draw
       Xanthous.Generators
@@ -100,11 +102,13 @@ executable xanthous
       Xanthous.Data
       Xanthous.Data.EntityMap
       Xanthous.Entities
+      Xanthous.Entities.Arbitrary
       Xanthous.Entities.Character
       Xanthous.Entities.Creature
+      Xanthous.Entities.Draw.Util
+      Xanthous.Entities.Environment
       Xanthous.Entities.Raws
       Xanthous.Entities.RawTypes
-      Xanthous.Entities.SomeEntity
       Xanthous.Game
       Xanthous.Game.Draw
       Xanthous.Generators