Adapt Postgres database driver

[manyuanrong]

Posgres database should be supported.
But wait until Deno's dynamic feature is complete.

[bartlomieju]

@manyuanrong let me know if you want to work on that, with joint effort we should be able to pull this off!

[manyuanrong]

@bartlomieju Yes, I want to have this feature. I haven't got the energy to start, but I've made a list.
#4