Many to Many Support

Hello,

I've created a minimal test to show how the library does not currently support many_to_many in Ecto schemas using the Northwind Demo. Here's the output:

I've also created a PR in hopes that I could get some guidance on how we might go about adding support for this feature.

The issue seems to be in that the build conditions function head is hard coded here:

etso/lib/etso/ets/match_specification.ex

Line 57 in f25bdea

    
           defp build_condition(field_names, _, {{:., [], [{:&, [], [0]}, field_name]}, [], []}) do

However it's not clear how I might change this to support many_to_many.

Please let me know if I can provide more information.

Thanks :)

I shall close this as the Pull Request as been opened.