Fix handling of JSON data

[baloo]

Introduced in 5.7.8

I chose not to handle charset parsing, all dict returned are in binary form. User is expected to parse it.

Fixes #181

[baloo]

This is a very rough implementation that misses a LOT of types but this gives a good starting point. Do not merge it yet.

[baloo]

https://github.com/percona/percona-server/blob/5.7/sql/json_binary.cc Here is the official "documentation" for mysql json type

[baloo]

@namabile I'd love if you could give this a shot before I merge it.

[namabile]

Awesome. I'll pull this later today and give it a shot.

[namabile]

Gave this a try and looks really good.

I hit an error on json types 4 and 5. Here are the cases I tested:

insert into test (id, value) values (1, 'true');
insert into test (id, value) values (1, '9');

Let me know if I can provide any info to help debug.

[baloo]

Well, those are easy to fix though. I intentionally left those one out. I though json was spec'ed as either an object or an array. No other structure. I just re-read the spec. I was wrong.
I'll fix those.

[baloo]

Here is a test for your last usecase @namabile

[baloo]

Hey @noplay, let me know what you think about this one.

[julien-duponchelle]

Sound good to me, thanks a lot for taking care of this one