Add solution to Sublist problem.

[ghost]

Why?

Solve unimplemented Sublist problem for Ruby.

What?

Sublist problem description: https://github.com/exercism/problem-specifications/blob/master/exercises/sublist/description.md

How Has This Been Tested?

rake test
rake test:sublist

Types of changes

• Add Sublist solution
• Add Sublist test case
• Add Sublist generator
• Add Sublist README
• Update config.json

[Insti]

Should also include instructions about how to run the tests.

[ghost]

I solved this problem once and for all by autogenerating READMEs: #721

[Insti]

This is a great PR, thanks.
It includes everything we need.

I love that you included a link to the canonical data 👍

I'd like us to implement this problem in a property based manner, see: exercism/problem-specifications#424 for how it was done with triangles.
This might be able to be done without a change to the canonical data.

[ghost]

I'd rather have the changes made to canonical data rather than make workarounds for it.

[Insti]

In which case we'll need to submit an issue/PR to the https://github.com/exercism/problem-specifications repository about that.