feat: support more Python sequence types when encoding to Protobuf

[hongquan]

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Fixes #20 🦕

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[hongquan]

@googlebot I signed it!

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[hongquan]

@BenWhitehead Could you please review?

[BenWhitehead]

@tseaver or @crwilcox Can either of you take a look at this and provide a review? This seems useful to me, but I'm not able to evaluate the code change toward the goal.

[crwilcox]

@hongquan would mind pulling in the upstream master and pushing again?

[hongquan]

@crwilcox I've just updated.