Introduce automatic schema generation after the migration applied

[kirillsalykin]

I think it would be helpful to have the schema of the entire database expressed via rust syntax, similar to what diesel provides,
something similar to this:

table! {
    posts (id) {
        id -> Int4,
        title -> Varchar,
        body -> Text,
        published -> Bool,
    }
}

this will open possibility to generate queries for inserts/updates/deletes.

what do you think?