Change StorageParser to an interface

src/main/java/earl/util/parsers/StorageParser.java

@@ -1,7 +1,7 @@
 package earl.util.parsers;
 
 /**
- * Class responsible for interpreting storage entries.
+ * Marker interface for parsers responsible for interpreting storage entries.
  */
-public abstract class StorageParser<T> implements Parser<T> {
+public interface StorageParser<T> extends Parser<T> {
 }

src/main/java/earl/util/parsers/TaskStorageParser.java

@@ -9,7 +9,7 @@
 /**
  * Class responsible for parsing stored entries of tasks.
  */
-public class TaskStorageParser extends StorageParser<Task> {
+public class TaskStorageParser implements StorageParser<Task> {
 
     /**
      * Returns a {@code Task} object based on the stored string.