Convert absurdctl to Go binary

[ruudk]

It currently requires python and psql to be installed. If you run PostgreSQL in Docker it won't work.

Since Habitat is already a Go program let's also make the ctl in go?

[mitsuhiko]

Yeah, I'm up for it. I was also thinking that it would be really nice if absurdctl could embed both the absurd.sql file as well as migrations, so that you could also use it to upgrade if you don't ship the migrations yourself. And the Go binary would make it very easy, whereas the current absurdctl tool doesn't really.