Complete rewrite, removed rspec-api-documentation

RSpec API has been rewritten from scratch, implementing the whole
DSL from `resource` to `request` and `respond_to`, in a way that is
compatible with the previous DSL but does not depend on rspec-api-
documentation.

This makes RSpec API more flexible in terms of what goes inside the
`it` blocks and how fixtures are created. Also, for the first time,
it supports not just local API (built with ActiveRecord and accessed
with RackTest), but remote API (accessed with Faraday)
Add accept_sort parameter: :attribute
Also test reverse sort with accepts_sort
Allow request with no description