* fix(macros): tell the compiler about external files/env vars to watch
closes#663closes#681
* feat(cli): add `migrate` subcommand for generating a build script
suggest embedding migrations on `sqlx migrate add` in a new project
- adds a -r flag whihc will create a reversible migration
- add revert subcommand, which reverts the last migration
- add --dry-run flag to migration run command, which list the migrations that will be applied
- updates add migration to check if all migration are of same type, i.e cannot mix and match reversible and simple migrations