-   Resolve ldiff output issues: Resolves #5 and #6 by adding system-output
    comparison calls to `bin/ldiff` compared against some pre-generated output.
    There is some timestamp manipulation involved with the output comparison,
    as the timestamps are unstable because of the way that git clone works.

-   Resolved a problem with bin/ldiff --context output.

-   Resolved a Numeric/Integer OptParse issue: later versions of Ruby had
    problems working with an `OptParse` option specification of `Numeric`; this
    has been changed to `Integer`.

-   This required some level of code remediation in the main library, but all
    tests now pass:

    -  Patchsets are now internally flattened one level explicitly, rather than
       using Array#flatten. This ensures that only the outer patchset array is
       flattened.

Fixes #48.

- Other linting configuration also applied.
- Soft-deprecating versions older than 2.3.

This reverts commits 01e0cae and 3b4d2be because they introduce fatally
breaking changes in the tests that were hidden by broken CI.

* 01e0cae: Add #to_ary to Diff::LCS::Change and Diff::LCS::ContextChange
  [Akinori MUSHA]
* 3b4d2be: Mention in rdoc that Diff::LCS::ContextChange can be converted to an
  array [Akinori MUSHA]

It would be quite handy if you could write as follows:

```ruby
Diff::LCS.sdiff(a, b).each do |action, (old_position, old_element), (new_position, new_element)|
  case action
  when '!'
    # replace
  when '-'
    # delete
  when '+'
    # insert
  end
end
```