remove unneeded `self` from config_attr macro
rework configuration_spec to test multiple invocations of `config_attr`

Previously only tested array-style invocations, eg `config_attr :foo, :bar` instead of

    config_attr :foo
    config_attr :bar
remove redundant Array cast in Configuration

Full Mutation-spec passing!
fix silly mistake in backend

This is why integration tests are important, and why I probably should have written one first.
ignore spec/integration/fixtures/*
fix type error when calling Rugged::Repository#write
fix logic error in Ramsey::Backend::Repo#git?
re-implement Ramsey::Backend::Repo#read to only retrieve object data

(not the whole Rugged Object)
clean up whitespace
remove #git?

It's a tautology anyway -- there is no way it will ever be false, since calling it
instantiates the repo.
first integration coverage on backend

Roundtrips data through the repo. This thing is neat.
refactor specs to look nicer
remove #exists?, #empty? from Ramsey::Backend::Repo

We didn't really need them, and it makes everything much simpler
add final case to backend integration spec
refactor backend integration spec
refactor configuration_spec a bit
Add some integration tests for Ramsey::Backend and refactor some other tests