Added various JSON features

+getAsJSONRoom method in RoomReader.java
+EnemyReader.java to read enemies from a JSON file
+JSONEnemy.java, the object of an enemy read from a JSON file
+JSONObject.java, an abstract class that represents any JSON object
+JSONUtil.java, containing a function to read JSONs from a file stream

*JSONRoom now extends JSONObject
Added ASCII mode

+ASCII textures for every sprite/tile
+Multiple textures allowed per entity
+Toggleable ASCII mode in-game
+enemies.json, the list of all enemies in the game which are loaded

*Implemented JSON reading for enemies