Show attribute details when composed have_attributes fails

[nellirx]

As requested in #759

For example
expect([person]).to match [have_attributes(:age => 10)]

Before
expected [#{object_inspect person}] to match [(have attributes {:age => 10})]

After
expected [#{object_inspect person}] to match [(have attributes {:age => 10} but had attributes {:age => 33})]

[JonRowe]

This is not the right approach to take, formatted_valuesis returning the wrong value for failure_message for the array case, thats what we need to fix, not changing the description that breaks the contract of our public matcher api.