Implement list ops exercise

[bgottlob]

Completes #192

[juhlig]

In reference to #278, please remove the Test versioning paragraph from README.md, as well as the version test related functions and definitions from the tests, example implementation, and module stub.

Instead, make a comment at the top of the test denoting the version of the canonical data in the problem specification that it implements (2.3.0 at the time of this writing) and the link to the raw data (https://raw.githubusercontent.com/exercism/problem-specifications/master/exercises/list-ops/canonical-data.json), like this:

%% based on canonical data version 2.3.0
%% https://raw.githubusercontent.com/exercism/problem-specifications/master/exercises/list-ops/canonical-data.json

[bgottlob]

I made those updates in a separate commit badee01

[juhlig]

Thanks :)