Format codebase and add support for multi-tenancy ..

[dlobo]

Needed to fork the repo again to add one more feature. We needed support to run the same migration again for a different tenant. This is especially important in the initial db seeding phase (not so sure if needed for later migrations, but we'll cross that bridge when we get there). Added a tenant column to the schema_seeds table to make this possible

also formatted the code using the built in formatter

if you are open to this being merged, I'll take a closer look at the PR, delete most of the commented code and do some more cleanup

[dlobo]

wondering if you have any thoughts or comments on these changes?

[dlobo]

Can you let me know either way. Working towards another version of the package that we'd like to publish on hexdocs.pm

lobo