Added AbstractPlaceholderExpansion for more readable expansion

src/main/java/me/clip/placeholderapi/expansion/AbstractPlaceholderExpansion.java

@@ -0,0 +1,30 @@
+package me.clip.placeholderapi.expansion;
+
+/**
+ * This is a convenient skeletal class for all plugins that want to supply placeholders.
+ */
+public abstract class AbstractPlaceholderExpansion extends PlaceholderExpansion
+{
+	private final String identifier, version, author;
+	
+	protected AbstractPlaceholderExpansion(String identifier, String version, String author) {
+		this.identifier = identifier;
+		this.version = version;
+		this.author = author;
+	}
+
+	@Override
+	public String getIdentifier() {
+		return this.identifier;
+	}
+	
+	@Override
+	public String getVersion() {
+		return this.version;
+	}
+	
+	@Override
+	public String getAuthor() {
+		return this.author;
+	}
+}