Add support for flattening arrays and change transforms arguments to …

[juanjoDiaz]

…an object.

Closes #401

In the future, I might enhance the flatten transform a bit more so you can specify the specific fields that you want to flatten (as in unwind).

[juanjoDiaz]

@knownasilya can you run the tests for this branch locally and give me some hint of what's going on?

All the tests pass just fine on my machine 😕

[knownasilya]

I get one failure

I'm on node 11.10.0

[coveralls]

Coverage remained the same at 100.0% when pulling f271275 on juanjoDiaz:improve_built_in_transforms into fae7166 on zemirco:master.

[coveralls]

Coverage decreased (-0.2%) to 99.752% when pulling c359cb3 on juanjoDiaz:improve_built_in_transforms into fae7166 on zemirco:master.

[juanjoDiaz]

All good now!
It was some weird old dependency in node_modules