Added a very detailed example

[PtrStruct]

I decided to add a visual representation of the difference between reference types & value types.
Show just how they work on the stack as well as on the heap.

Summary

Describe your changes here.

Fixes #Issue_Number (if available)

[dnfclas]

All CLA requirements met.

[pkulikov]

@PtrStruct @BillWagner I have several concerns about this PR:

• there should be (I don't know if such already exists) an article in the C# programming guide that explains difference between value and reference types. Then, that article can be linked from the C# reference topics (from both value type and reference type topics). The example from this PR would fit that article.
• explanation should be moved out of comments to the text that explains the example. That makes localization possible.
• at last, stack and heap (the implementation detail) can be omitted when describing the difference between value and reference types. Check related discussion in the following issue: Do not claim that structs are on the stack #4561 (especially this comment of @BillWagner)

[PtrStruct]

@pkulikov I did look around the msdn and after doing so, I found this article to be the most fitting one.
There was one showing both types and minor differences, but that was for Visual Basic.
I am making some changes regarding your concern with the comments not being text.

[BillWagner]

@PtrStruct

Thank you for adding this. However, as @pkulikov mentioned, there are a number of concerns.

First, this example and the introduction in the article on classes and structs covers much of this information.

Second, as I stated in this comment value types are "on the stack" except when they aren't. They aren't on the stack when they are members of a reference type, in an array or other collection, captured by a closure, and so on. Your explanation is correct for the cases it covers, but it is misleading by not discussing those other cases.

I suggest we close this PR, you look at the classes and structs article referenced above. Then, if there is important information that you feel is lacking, submit a PR updating that topic.

What are your thoughts?

[PtrStruct]

I understand, thanks.
You may close this PR.

[BillWagner]

Thanks @PtrStruct

I'll close this.