Refactor redis keys and store messages in protobuf

Changes:
- Task messages are stored under "asynq:{<qname>}:t:<task_id>" key in redis, value is a HASH type and message are stored under "msg" key in the hash. The hash also stores "deadline", "timeout".
- Redis LIST and ZSET stores task message IDs
- Task messages are serialized using protocol buffer

.gitignore

@@ -18,4 +18,7 @@
 /tools/asynq/asynq
 
 # Ignore asynq config file
-.asynq.*
+.asynq.*
+
+# Ignore editor config files
+.vscode