Add comments to json.go

[gfr10598]

I haven't figured out how to suppress warnings from golint. Various urls suggest that //nolint or // nolint should work, but they do not.

We may actually be able to change the names to use camelCase, but for now let's leave them as is, and tolerate the warnings until we can figure out how to suppress them.

There are no code changes aside from renaming RTT and TTL, so go vet and travis tests are sufficient to ensure correctness.

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This change is 

[SaiedKazemi]

Yeah, I was also looking into how we can tell golint to ignore certain errors but couldn't find anything that would work for me.

[coveralls]

Pull Request Test Coverage Report for Build 121

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.27%

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Totals
Change from base Build 118:	0.0%
Covered Lines:	1069
Relevant Lines:	1099

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💛 - Coveralls