Improvement list

[gshipunov]

Some minor problems I came across while reviewing #23

• all the config env vars need to be prepended with DATACARE_, so there's no conflicts if services are run in the same environ
• If prometheus endpoint fails, datacare panics. Maybe worth just log it and forget about it.
• CORS just allows everything at the moment
• #![deny(missing_docs)]
• #![warn(rustdoc::broken_intra_doc_links)]

I guess this can be left alone for now, but we need to get back to it after the feature freeze. If you see any other rough edges, plz append to the list above