Add PonyCheck to the tutorial

[SeanTAllen]

No description provided.

[SeanTAllen]

Per the RFC, this content is repurposed from the PonyCheck README.

I'm trying to find a couple of good "introduction to property based testing" resources to include as well with the target audience of "people who know unit-testing and either don't know what property-based testing is or have heard of it but have never done it".

[SeanTAllen]

This will fail checks until the Ponyc PR is merged.

Also requires the PonyTest rename to be merged.

[SeanTAllen]

Shouldn't be merged until after pony 0.49.0 has been released.

[rhagenson]

I took a look at the raw file in addition to the diff. Raw file changes outside the diff are commented about below:

• "Property based Testing first came up as..." -> "Property based testing first came up as..." i.e. lowercase "t"
• "A Property needs a name" -> "A Property1 needs a name" ie add the "1"
• "Below is a classical List reverse properties from the QuickCheck paper adapted to Pony Arrays" -> "Below is a classical List reverse properties from the QuickCheck paper adapted to Pony Arrays" ie add the code formatting for referenced data structures (or lowercase them so it is simply list and arrays which, to me, would then be generic and need no special formatting)
• Many of the links are/will be broken right now, referring to addresses such as https://stdlib.ponylang.io/PonyCheck-Property1 rather than https://stdlib.ponylang.io/pony_check-Property1 ie correctly adding the underscore in "pony_check" per the rename

[SeanTAllen]

@rhagenson can you do suggested changes for fixes or go ahead and edit directly and push?

[rhagenson]

I can, yes. Give me a couple minutes to hop back on my laptop and the changes will be in place.

[SeanTAllen]

I made what I could figure out.

[rhagenson]

I will take a look now and push any remaining changes.

[rhagenson]

@SeanTAllen My edits are in place now. You fixed much of what I had suggested as fixes already, but I found some inconsistencies in the URL used for the stdlib (.io versus .org), made a consistency edit to name PropertyHelper parameters the same across this page (as ph rather than h), and modified the language to avoid having to say "UnitTests" then linking to a page for singular "UnitTest" page.