Upgrade to rspec-rails 3.x.x

    config.infer_spec_type_from_file_location!

Gives us spec types for free, like `type: :controller` or `type: :feature`.

    config.treat_symbols_as_metadata_keys_with_true_values = true

Defaults to true in RSpec 3.
Remove Brewfile, document laptop setup

There was a Brewfile template in the Suspenders source that was not being used
when generating an app. Rather than maintaining it, it might be better to
document for app developers that they should set up their machine using
something like thoughtbot/laptop.
Remove Foreman from Gemfile

Provide documentation in project's README and in `bin/setup`.

https://github.com/ddollar/foreman/pull/437#issuecomment-41110407
Raise on missing translations in development/test

Lessons learned from http://robots.thoughtbot.com/foolproof-i18n-setup-in-rails
Move Formulaic into Features module