Occassionally cull the ponies cache of unused values to prevent a gradual increase in memory usage

src/main/java/com/minelittlepony/pony/data/Pony.java

@@ -42,11 +42,22 @@ public class Pony implements IPony {
     private final ResourceLocation texture;
     private final IPonyData metadata;
 
+    private long expirationPeriod;
+
     public Pony(ResourceLocation resource) {
         texture = resource;
         metadata = checkSkin(texture);
     }
 
+    boolean hasExpired() {
+        return expirationPeriod <= System.currentTimeMillis();
+    }
+
+    Pony touch() {
+        expirationPeriod = System.currentTimeMillis() + 30000;
+        return this;
+    }
+
     private IPonyData checkSkin(ResourceLocation resource) {
         IPonyData data = checkPonyMeta(resource);
         if (data != null) {

src/main/java/com/minelittlepony/pony/data/PonyManager.java

@@ -49,7 +49,7 @@ public class PonyManager implements IResourceManagerReloadListener, ISkinCacheCl
 
     private PonyConfig config;
 
-    private Map<ResourceLocation, IPony> poniesCache = Maps.newHashMap();
+    private final Map<ResourceLocation, Pony> poniesCache = Maps.newHashMap();
 
     public PonyManager(PonyConfig config) {
         this.config = config;
@@ -61,7 +61,11 @@ public class PonyManager implements IResourceManagerReloadListener, ISkinCacheCl
      * @param resource A texture resource
      */
     public IPony getPony(ResourceLocation resource) {
-        return poniesCache.computeIfAbsent(resource, Pony::new);
+        IPony result = poniesCache.computeIfAbsent(resource, Pony::new).touch();
+
+        poniesCache.entrySet().removeIf(entry -> entry.getValue().hasExpired());
+
+        return result;
     }
 
     /**