Add javadoc descriptions for all classes

src/main/java/com/technicjelle/BMCopy.java

@@ -24,6 +24,9 @@
 import java.nio.file.StandardOpenOption;
 import java.util.function.Consumer;
 
+/**
+ * Utility functions for copying stuff to BlueMap
+ */
 public class BMCopy {
 	private BMCopy() {
 		throw new IllegalStateException("Utility class");

src/main/java/com/technicjelle/BMSkin.java

@@ -24,6 +24,9 @@
 import java.util.Optional;
 import java.util.UUID;
 
+/**
+ * Utility functions for BlueMap skins and playerheads
+ */
 public class BMSkin {
 	private BMSkin() {
 		throw new IllegalStateException("Utility class");

src/main/java/com/technicjelle/ShapeExtensions.java

@@ -16,6 +16,9 @@
 import de.bluecolored.bluemap.api.math.Shape;
 import org.jetbrains.annotations.NotNull;
 
+/**
+ * Utility functions for {@link Shape}s
+ */
 public class ShapeExtensions {
 	private ShapeExtensions() {
 		throw new IllegalStateException("Utility class");