go(subroutines) ALL the things!

- Moving the writer to subroutines
- Clean the code around the creation of file and paths
- CREATE & INSERT are run inside a transaction now
- all the "own type errors" got removed -> recommended by a proper
  Gopher
- the flags reading was moved to the main() -> recommend by the same
  Gopher (hi @campoy!)
- polo executable was also added to the ignore files.

WIP: it looks like the subroutines try to read the "files" table in the
sqlite/memory after it's deleted. But, I honestly don't know where this
DB gets auto-deleted, event with Sleeps for testings it continue
breaking.