crypto-square: Reflect changes to problem specifications

[nholden]

Why?

We recently made some changes to the crypto-square exercise over in exercism/problem-specifications to stop testing intermediate functions, fix inconsistencies in the description, and generally improve tests.

Bringing our tests and README inline with the new specifications would address #422, #545. Using a generator to do so would help us with our goal of generating all exercise tests.

What?

This PR:

• Adds a test generator for crypto-square
• Generates tests for crypto-square from the canonical data
• Updates the example solution to reflect the changes to the specification
• Updates the README to reflect changes to the specification

How Has This Been Tested?

I ran the updated example solution against the newly generated tests and they passed.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Breaking change (fix or enhancement that would cause existing functionality to change)
• Gardening (code and/or documentation cleanup)

References and Closures

Closes #422 and #545.

Checklist:

• I have read the CONTRIBUTING document.
• My change relies on a pending issue/pull request
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[Insti]

This looks great, thanks @nholden I'll have a closer look at it when I can find some time in the next day or so.

[nholden]

Just a heads up: I'll be off the grid for a bit, so if there are any requested changes to this PR, feel free to go ahead and make them without me if you'd like, or I'll be happy to loop back in early November.

[Insti]

Thanks @nholden ❤️