Make event_store Mix task logic available independently of Mix

[uberbrodt]

Distillery releases do not have Mix or the commandline tool mix available. In order to better support this deployment option, it would be useful to have the functionality of the following tasks available without any Mix dependencies:

• event_store.create
• event_store.drop
• event_store.init
• event_store.migrate

[bamorim]

@uberbrodt how things are going with this? Are you thinking about implementing it?

Some people commented on #22 that one idea would be to use Ecto as a backend.

Since Ecto already has the concepts of migrations, this might solve the problem with the event_store.migrate piping to psql.

It should also be more straightforward to solve #73 and #76.

This would also be great for testing since we could use Ecto.Sandbox.

My only concern with that is that this would increase the dependencies.

[uberbrodt]

@bamorim I think I will have time soon to look at this again and do a PR. One question I have, is do we need to be able to rollback migrations? Currently you can only go forward, which is probably fine, but I suppose there might be a case where rollback would be handy.

[slashdotdash]

@uberbrodt The migration scripts are created by hand, there's no support for rollback. Instead you'd need to take a backup of the database before migrating and restore the backup to go backwards.