Reflect the differences between the Solidity standard-json and the metadata.json's settings field

[kuzdogan]

We realized a while ago that the settings field in the metadata.json does not fully reflect the Solidity standard-json input and has a differing field compilationTarget. This should be noted in the metadata docs where it says "Reflects the settings in the JSON input".

Also how the libraries are formatted in the metadata and the standard json differs, as discussed in #1370 This should also be noted in the metadata docs.