I think it might be worth extracting everything passed into `prepare_submatcher` here out so that we avoid duplication and such long lines.

How about something like the following?:
```ruby
def comparison_matcher_for(value, comparison)
  NumericalityMatchers::ComparisonMatcher
    .new(value, comparison){ @diff_to_compare }
    .for(@attribute)
end
```

And the above would look something like:
```ruby
def is_greater_than(value)
  prepare_submatcher comparison_matcher_for(value, :>)
end
```

Is this overkill? @drapergeek @mcmire