Proto commits in hibiken/asynq

These 4 commits are when the Protocol Buffers files have changed:

Commit:401f7fb
Author:Ken Hibino
Committer:Ken Hibino

Add GroupKey field to TaskMessage

The documentation is generated from this commit.

Commit:f4ddac4
Author:Ken Hibino
Committer:Ken Hibino

Introduce Task Results * Added Retention Option to specify retention TTL for tasks * Added ResultWriter as a client interface to write result data for the associated task

Commit:62168b8
Author:Ken Hibino
Committer:Ken Hibino

Add LastFailedAt field to TaskMessage

Commit:7af3981
Author:Ken Hibino
Committer:Ken Hibino

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