Support nested keys

[eevleevs]

Allows body['query.filtered.query.match.description']

[eevleevs]

Partially covers #110

[mewwts]

Thanks for your contribution @eevleevs!

Will this be backwards incompatible?

[eevleevs]

Could be, if one used keys including a dot until now.
But that would be a strange use case, since those keys cannot not be accessed using dot notation.

[partic2]

In javascript. user can use keys including dot, So I think we should not prevent user do that here either.

Maybe another function body.chain_get('query.filtered.query.match.description') is beter, Or test if raw key is exists before parse keys into nested get?

I'm not the maintainers, just in my humble opinion.