Fixes #1007, Add lowdb support

[gutenye]

I've a few questions and left notes in code.

Maybe we can extends builtin gatsby-transfomer-json with {"posts": [{"value": "a"}, ..]} support instead of a new package.

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[KyleAMathews]

I think putting this in its own package makes the most sense as there's an infinite number of ways JSON can be structured so trying to support those all in gatsby-transformer-json won't work.

Also with each transformer type being its own package, they'll be easy to find via Google or the Gatsby website.

Could you just add your questions here as a comment please.

[gutenye]

@KyleAMathews
Okay, I'll create a new package.

What's children and parent used for in createNode()?
It seems works fine when I provide empty array for children and dummy id for parent.

[KyleAMathews]

@gutenye they're useful conventions not a hard things-will-break-without-them requirement. They're there so that you can write queries following the transform chain. It's often useful for example to jump up from a transformed node to its file parent to get file specific information e.g. its size or file name, etc. I sometimes write queries too where I query for files and then jump to the right child.

So it's strongly encouraged you add them.

[gutenye]

Published: https://github.com/gutenye/gatsby-transformer-lowdb

[KyleAMathews]

Looking good!

FYI, there'll be some breaking changes for the API soonish see #858

Should be a pretty easy upgrade.

[gutenye]

@KyleAMathews Thanks for the heads up.