pg-promise updates

[vitaly-t]

To my recollection, this library was kind of inspired from using pg-promise, and it still uses it as the main reference, although a very old version of it.

Version 9.3 of pg-promise kind-of opened the floodgate to supporting BigInt natively all the way through. And a library such as schemats should somehow keep up with that, in order to stay relevant.

Just a thought 😄