Clarifications around plugin message API.

api/src/main/java/com/velocitypowered/api/proxy/messages/ChannelIdentifier.java

@@ -1,7 +1,7 @@
 package com.velocitypowered.api.proxy.messages;
 
 /**
- * Represents a kind of channel identifier for use with plugin messaging.
+ * Represents a channel identifier for use with plugin messaging.
  */
 public interface ChannelIdentifier {
 

api/src/main/java/com/velocitypowered/api/proxy/messages/ChannelMessageSink.java

@@ -1,7 +1,7 @@
 package com.velocitypowered.api.proxy.messages;
 
 /**
- * Represents something that can send plugin messages.
+ * Represents something that can be sent plugin messages.
  */
 public interface ChannelMessageSink {
 

api/src/main/java/com/velocitypowered/api/proxy/messages/ChannelMessageSource.java

@@ -1,7 +1,7 @@
 package com.velocitypowered.api.proxy.messages;
 
 /**
- * A marker interface that indicates a source of plugin messages.
+ * Indicates that this may be a source of plugin messages.
  */
 public interface ChannelMessageSource {
 

api/src/main/java/com/velocitypowered/api/proxy/messages/LegacyChannelIdentifier.java

@@ -14,6 +14,11 @@ public final class LegacyChannelIdentifier implements ChannelIdentifier {
 
   private final String name;
 
+  /**
+   * Creates a new legacy channel identifier.
+   *
+   * @param name the name for the channel
+   */
   public LegacyChannelIdentifier(String name) {
     Preconditions.checkArgument(!Strings.isNullOrEmpty(name), "provided name is empty");
     this.name = name;