Add a Rake task to build the Yard docs
Fix the deep_eql RSpec matcher

It did not detect the case where one hash has a key with value nil, and
the other does not have the key.

    { foo: nil }

vs

    { }
Documentation fixes/improvements

Decided to stick with the ROM style of @param [Class] name for YARD
docs. YARD also supports @param name [Class], but I prefer this
one. Start the description with a capital or, even better, move it to
the next line and indent.

    # @param [Beverage] tea
    #   The tea you like to brew

This commit is just a nudge in the right direction.
Remove the old `after' hook, we have better hooks in place now.
Use `format_name` instead of just `name` for the name of format class

Format implementations know their own "system name",
e.g. Yaks::Format::JsonAPI.format_name == :json_api

Before we used simply `name' for that, but that clashed with Ruby's
Class#name method.
Improve mutation coverage, upgrade to RSpec 3

A slew of fixes to get to better mutcov, back at ~93% now. Also made the
change from RSpec 2.99 to RSpec 3, we were already mostly compatible.