Add `adb features`.

Shows the features supported by the active adb server.

Change-Id: I4a58a2ca082823c43f7a49e2c62ff80df6426756
diff --git a/adb/commandline.cpp b/adb/commandline.cpp
index 1c5b5bd..c7b7675 100644
--- a/adb/commandline.cpp
+++ b/adb/commandline.cpp
@@ -1460,6 +1460,9 @@
         fprintf(stdout, "%s", adb_version().c_str());
         return 0;
     }
+    else if (!strcmp(argv[0], "features")) {
+        return adb_query_command("host:features");
+    }
 
     usage();
     return 1;