JSON parsing and printing for messages

[siddharthab]

Resolves #61.

[eddelbuettel]

Nice work -- the PR looks very clean. I will take another, closer, look later.

[eddelbuettel]

I made a minor local commit to get rid of two warnings under R CMD check but as I can't push that back to you I will just merge and proceed. Hope that is ok.

[siddharthab]

Thank you for the quick review.

[eddelbuettel]

My pleasure -- thanks for the PR. I tend to get to get to things sooner, but I had a distration from a Rcpp release which may need a follow-up given an issue on macOS we did not catch / could not catch for lack of reverse-depends checking infrastructure on macOS :-/ Plus an issue with BioConductor which I may have to add to the test matrix...

I presume you looked at my follow-up commit and have no issues? I added you to ChangeLog too.

[siddharthab]

Thanks! The changes in the follow-up commit look good.

The next thing I would like to add when I have the time is to return a helpful message when people mistype field names instead of segfaulting.

[eddelbuettel]

Having slept over it, I think I will restore the small 'if open' change.

Catching such a segfault would be awesome! I'll release this as an interim version with JSON support.

[eddelbuettel]

I just looked at it in more detail. Removing the condition in the readASCII case literally the last thing I did -- it must have come up when I switched the tests from RUnit to tinytest revealing some more verbosity. Hence, let's keep it as you amended it. As in readASCII. If it barfs we can adjust.

[siddharthab]

Sounds good.