Added Rawable interface (#2370)

* Added Raw interface

  Jedis should have a common interface to represent all commands and keywords (and, perhaps, arguments). Closest thing we currently have is `ProtocolCommand` interface. But the problem is that it contains the word COMMAND which would be misleading to use for something other than commands.

  One option is to rename the existing interface. But this would be a breaking change and so it can't be available before at least Jedis 4.0. Even that can be received negatively by the users who could be using the existing interface.

  Having a parent interface, on the other hand, does not have such issues and can be included in upcoming non-major release.

  I went with name `Raw`, instead of other names like `ProtocolKeyword` or `ProtocolArgument`, because it is short and fits nicely with our go to method `getRaw()`.

* dedicated package

  I have also put it in a separate package because with growing number of classes, we'd be able to put some classes in that package.

* Rawable

  `Raw` in now `Rawable`. Idea courtesy goes to @gkorland.

Author: sazzad16

src/main/java/redis/clients/jedis/Protocol.java

@@ -5,6 +5,7 @@
 import java.util.List;
 import java.util.Locale;
 
+import redis.clients.jedis.args.Rawable;
 import redis.clients.jedis.commands.ProtocolCommand;
 import redis.clients.jedis.exceptions.*;
 import redis.clients.jedis.util.RedisInputStream;
@@ -275,7 +276,7 @@ public byte[] getRaw() {
     }
   }
 
-  public static enum Keyword {
+  public static enum Keyword implements Rawable {
     AGGREGATE, ALPHA, ASC, BY, DESC, GET, LIMIT, MESSAGE, NO, NOSORT, PMESSAGE, PSUBSCRIBE,
     PUNSUBSCRIBE, OK, ONE, QUEUED, SET, STORE, SUBSCRIBE, UNSUBSCRIBE, WEIGHTS, WITHSCORES,
     RESETSTAT, REWRITE, RESET, FLUSH, EXISTS, LOAD, KILL, LEN, REFCOUNT, ENCODING, IDLETIME,
@@ -294,6 +295,7 @@ public static enum Keyword {
       raw = SafeEncoder.encode(this.name().toLowerCase(Locale.ENGLISH));
     }
 
+    @Override
     public byte[] getRaw() {
       return raw;
     }

src/main/java/redis/clients/jedis/args/Rawable.java

@@ -0,0 +1,6 @@
+package redis.clients.jedis.args;
+
+public interface Rawable {
+
+  byte[] getRaw();
+}

src/main/java/redis/clients/jedis/commands/ProtocolCommand.java

@@ -1,7 +1,6 @@
 package redis.clients.jedis.commands;
 
-public interface ProtocolCommand {
-
-  byte[] getRaw();
+import redis.clients.jedis.args.Rawable;
 
+public interface ProtocolCommand extends Rawable {
 }