Convert hashes to indifferent access

[tfausak]

Fixes #164.

>> Class.new(ActiveInteraction::Base) { hash :h, strip: false; def execute; h['foo'] end }.run!(h: { foo: 'bar' })
=> "bar"

Can you review this, @AaronLasseigne?

[tfausak]

This should be merged into the v2.0.0 branch, which doesn't exist yet.

[AaronLasseigne]

I think we'll want to remove stringify_the_symbol_keys and as a result of that, transform_keys.

[tfausak]

👉 #215