Add user-properties functionality

[ihandley]

This addition allows the package to support user properties as seen in the Message class from the com.aliyun.openservices ons.api Java library. We have a client who uses this library to interact with rocketmq and wants to pass certain meta-data using user-defined properties.

[codecov[bot]]

Codecov Report

Merging #102 (3ee239f) into master (6d8bde1) will decrease coverage by 32.31%. The diff coverage is 87.50%.

:exclamation: Current head 3ee239f differs from pull request most recent head 582d79f. Consider uploading reports for the commit 582d79f to get more accurate results

@@             Coverage Diff             @@
##           master     #102       +/-   ##
===========================================
- Coverage   91.75%   59.44%   -32.32%     
===========================================
  Files          35       35               
  Lines        2148     2155        +7     
  Branches      354      354               
===========================================
- Hits         1971     1281      -690     
- Misses        177      874      +697     

Impacted Files	Coverage Δ
lib/producer/mq_producer.js	41.72% <0.00%> (-51.00%)	:arrow_down:
lib/message/message.js	88.40% <100.00%> (-11.60%)	:arrow_down:
lib/store/remote_broker.js	16.47% <0.00%> (-80.00%)	:arrow_down:
lib/process_queue.js	16.12% <0.00%> (-61.30%)	:arrow_down:
lib/producer/topic_publish_info.js	36.36% <0.00%> (-54.55%)	:arrow_down:
lib/mq_client_api.js	21.75% <0.00%> (-54.20%)	:arrow_down:
lib/consumer/mq_push_consumer.js	42.10% <0.00%> (-51.20%)	:arrow_down:
lib/channel.js	55.17% <0.00%> (-44.83%)	:arrow_down:
lib/mq_client.js	54.90% <0.00%> (-34.97%)	:arrow_down:
... and 7 more

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[denghongcai]

how about add getUserProperties method? i think setUserProperties will be happy to have a mate. 😄

[ihandley]

how about add getUserProperties method? i think setUserProperties will be happy to have a mate. 😄

Done.