This will be run at compile time - the goal is to generate a build-
metadata.json file with a bunch of useful facts about the databases that could
be expensive to generate at run-time.
Example metadata:
{
"flights": {
"file": "flights.db",
"tables": {
"airlines": 6048,
"airports": 8107,
"routes": 67663
},
"hash": "07d1283e07786b1235bb7041ea445ae103d1571565580a29eab0203c555725fd"
}
So far we have a sha256 hash of the database file itself, plus a row count for
each table.
Fixes#11
